Automotive Repair: Electrical Troubleshooting Tips and Techniques with Joe Glassford

Automotive Repair: Electrical Troubleshooting Tips and Techniques with Joe Glassford


hey everybody this is Pete Meyer Motor Age magazine welcome to after-hours if this is your first time here and want to take the opportunity again to thank you for coming out to hang out with us after hours is a really informal webinar that we do every second and fourth Tuesday and we bring in a variety of industry experts on a variety of topics that we think would be of interest to you I want to introduce our guest tonight mr. Joe Glassford Joe how are you I’m doing fine and welcome well side note here guys there’s a chat window to the right side of the player so if you have any questions for either Joe or myself please use the chat function there we will try to keep up with that if you have any issues I think we have all the audio and video bugs worked out yes a little volumes moving so you should be able to hear us okay tonight’s topic that that Joe is absolutely an expert in is electoral troubleshooting we know that gives a lot of guys fits me included and I know that it’s something that though once you get it you really realize that it’s not it’s not that complicated as a job no it’s not once you understand the basics of it and it really is not it’s just misunderstood I think a lot of it I know that in the shop we used to call it FM I don’t know if it would be apropos to define what FM stands for on a webinar I mean there’s nobody that’s an r-rating here somewhere there right and and and so we don’t take up and waste any of your viewers times we’re going to go right ahead over to Joe’s presentation again if you have any questions while while Joe’s talking to us tonight out of the chat window and I’ll keep an eye on that and and we’ll go from there so Joe Carroll transition Joe I’m going to come bring you down a bit and start your presentation up all righty and get everybody focused in so they can see it real good and if if you’re new again to after-hours you or have been here before you know that guys it is just me doing all the camera work so let me get that set up there we go whoa back that out a little bit a little bit more and I think we are there Joe it is all yours okay well thank you very much I really appreciate you allowing me the opportunity to talk on the subject that said I’ve been dealing with for the last 25 years okay I started out fixing a one cylinder lawn mower many many years ago didn’t know much about voltage drop testing until I got involved in heavy to actually troubles do some troubleshooting but I think the concept of voltage drop testing is just misunderstood and so what I like to do is to get you involved in what you’re up against okay we can go on from there okay go okay all right yeah now I’m only saying not about 3/4 of the screen on mine maybe I’m not sure if that’s the way it’s is working everywhere else no no don’t worry about the camera you’re looking at buddy that’s a whole different viewpoint okay I’m sorry it’s all new all new technologies are making okay most of the information that I’m presenting tonight is actually out of my my latest book the hands-on vehicle testing reference which is available on my website of course we’ll go on from there enough plug in my product oh no dude and I’m going to point out for the guys to please make a note of that that website address get a chance to check it out when you can I’ve seen and and gone through Joe’s book it is a very handy guy to keep in your toolbox so by all means check that out if you study the chemistry of batteries and I don’t know exactly how it came about but each cell of a battery has 2.1 one volt potential and the 12 volt battery has six cells so if you do the math a 12-volt batteries is fully charged as 12 point six six volt potential and that’s what you want that’s what you’d like to see available to all the loads on the vehicle every load on the vehicle ought to operate as if it’s hot-wired across the positive and negative terminals of the battery okay go from there well if we know what voltage is then what is voltage drop let’s take a look at that next okay it’s it’s just the voltage drop is nothing more than the difference between your fully charged source voltage and the voltage potential that’s available to any load on the vehicle okay now the the voltage is going to drop due to some very common causes all right the first one of course are the loads the engineered loads that’s the light bulb that’s the fuel injector that’s the fuel pump that’s all the things we operate on the vehicle those are the engineered loads that the reason we have loads on the vehicle is to get work done doesn’t matter what it is even electric sheets seat heater brake light control module those are all loads okay go ahead so that these are some things that cause voltage to drop now ideally we want all the boulders to drop across the engineered loads it doesn’t always happen there are some engineered resistances we’ll see an example that tonight there are some resistances that Engineers put in the in the circuit if you’ve been around a long time you remember the ballast resistors used to use on the old ignition coils that was an engineered resistance it dropped the voltage to a six volt coil from a 12-volt battery it’s an engineer lots of engineered resistances all of the control modules we use today have engineered resist we’re still looking at what causes source voltage to drop airspace in any current path airspace loose connections connections are critical we’ll take a look at that in detail here shortly okay and then non conducting material in a path I’m talking about a current path I troubleshoot current paths that don’t troubleshoot circuits you stay focused on a current path and we’ll be looking at that a little bit here corrosion the non conducting material in a path that’s one thing and another problem that can cause source voltage to drop would be electrolysis and it’s a it’s a pretty sophisticated word but it’s nothing more than a chemical reaction that occurs between dissimilar metals and we’ll take a look at that also okay alright first of all now we we’re looking at we’re looking at what we’re gonna look at what causes source voltage full fully charged battery voltage to drop and first of all engineered voltage drops all right here’s a basic circuit I got a battery I got some kind of a load the drawing shows that it’s some kind of a motor that could be a light bulb it could be anything and then it has a path back to the battery the ground symbol is nothing more than the negative side of the battery okay now this is a simple circuit I like the kiss method you know keep it simple Stanley and this is a hot-wired circuit there’s no switches in here there are no fuses in here this is theoretically the way every loan on the vehicle should operate as if it’s hot-wired across the battery terminals okay now that’s an if we put in an engineered there are no voltage drops here is just wire batteries if we go to the next slide you’ll see what happens when we put in an engineered voltage drop okay it’s the same load I’ve got a switch I switched it over to low speed now the current path has to go from the battery through a engineer sister and instead of a single load circuit that’s going to take all of the voltage we just created a series circuit the load and we and the resistor which basically is a second load in series with the first load so not all of the voltage across the battery can drop across the load some of its going to drop across that resistor and this thing is going to operate at lower speed there’s all kinds of engineered voltage drops on vehicle ok well we’re going to be looking for are the non engineered voltage drops okay all right now the next slide I’m still talking about what’s causes source voltage to drop and they I like to think of I like to think of voltage drop as a maintenance pressure you can click on there okay alright that’s just a term that makes me think about what voltage drop is voltage drop to me is a maintenance pressure required to overcome resistance now you want to click on again the resistance in this connection is nothing more than air space air space is a resistance in any circuit if we have a solid piece of wire the full length of the wire has no air space it just has electrons it can move from one end to the other but we have all kinds of connections involved this is where you run into problems because the the voltage drop is a maintenance pressure used to overcome the resistance of the air space in any connection on the vehicle okay now let me see let’s go to see what we’re talking about here you want to take a look at this slide and I’ve got I’ve got a voltmeter set up to read click on one more we click up okay there you go set up to read millivolts okay and I’ve got the positive volt meter probe connected to a back it’s the positive battery cable connected to a Beck which is a bus electrical connector general motors use an under view okay in addition to that I’ve got the negative terminal of the voltmeter touching the top of the positive terminal and look what I’m reading you want to click on another one for me okay now that I’m reading in millivolts that’s point two millivolts and that’s that the reading is its point zero zero zero two zero zero volts that’s 200 microvolts what’s that mean right now I’m reading two hundred one millionth of a volt it’s absolutely inconsequential but it is a voltage drop what’s causing the voltage drop okay why is it doing that alright it’s doing that because it’s it’s a maintenance pressure that’s required to overcome the air space these microscopic peak and Valley of the metallurgy between those two probes and the metal of the probe touching the BEC connector on the on the cable right there okay so now that’s one reading all right now look look where my on the next slide look or my my probes are my probes are still touching the one that I clipped on is still clipped on but the negative probe is just a short distance you want to move your head there okay and one more I’m still reading millivolts okay but I’m reading 1.3 millivolt why is that go ahead it’s because it’s a maintenance pressure required to overcome the resistance in the air space between the metal and the probe and the metal it’s touching plus the distance one more okay that’s and that’s why this what made me start thinking about voltage drops nothing more than a maintenance pressure it has to overcome resistance and it has to overcome that airspace all right now here we’ve got another slide and if you look at where my probes are I’ve still kept the positive probe clipped to where it was originally but I moved my negative probe beyond the connection go ahead my reading now jumps up to three point one millivolt and why is that it’s the air space it’s the maintenance pressure required to hit required to overcome air space now what air space the air space and the metal of the probe and the metal it’s touching and the metal of the negative probe and the metal it’s touching plus the distance between the two plus the air space in the connection now if that connection was loose that voltage drop would be much higher than it is this is a good tight connection in consequential okay and one more connections are critical we got to pay attention to connections they will absolutely drive you crazy okay go on from there all right now we’re still looking at what causes source voltage to drop airspace I looked at that now we’re looking at corrosion you’ve seen this this is just a corroded connector off of some component that had a run for a while and you run into this all the time so this is a non conducting material you know we want electrons to travel through conductors and the non conducting material in any path corrosion of any kind of course is going to cause us to maintain a pressure in the current path at that point to overcome that resistance okay all right now this is a electrolysis we’re still looking at things that cause voltage to drop electrolysis I’m always intrigued by the side mount battery post or battery connection if you will look what we got we got a bolt coated with some kind of metal you speak and Miam but I hear now that that’s too expensive so they’re used some other alloys then you got copper then you got lit you put all three of these together you are guaranteed to have electrolysis electrolysis is nothing more than a chemical reaction between dissimilar metals that have electrons running through them that’s that thing has to be cleaned up taking take a look at that thing on any side mount sugar okay so what are we doing what are we going to be spending our time troubleshooting we’re always going to be looking for unwanted non-engineered voltage drops okay oh yeah and how are we going to do that we’re going to start with a good meter you got to have a good meter to do good voltage drop testing well let’s look at the accuracy of a meter all right a very good meter which is which we consider today to be the best now this is not I’m going to say this is the best because within our price range a point one percent accurate meter is excellent for the type of work you guys do okay but there are meters out there that more are more accurate than 0.1% but they’re also very very expensive and we don’t need them you know now you want to check the owner’s manual under DC voltage accuracy if you don’t know how accurate the meter you own is now if you don’t have the owner’s manual the nice thing about today’s technology you can Google generally Google the manufacturer you can download the manual that’s a possibility okay now an accuracy of 0.1 percent being the best let’s say that we had a charging voltage there have 14.3 the vehicles running alternator’s charging the battery at fourteen point three volts if you have a point one percent accurate meter which is the best the meter could read on the high side plus point one percent remember now the actual voltage is fourteen point three volt charging that meter could read 14.3 1 on the high side and 14.2 9 on the low side and it go ahead it would actually be off the actual again by 14 millivolts that’s 14 1070 and we think it in our technology today we don’t need anything more accurate than that for the type of work that we do go ahead alright now if you let’s say that you have a a 1 percent accurate meter charging voltage same as before 14.3 on the high side you could read 14.4 4 and on the low side now we’re talking plus or minus 1% of what the actual reading is you’d be off the actual by a hundred and forty three millivolts okay now the next one some of the sensor grounds that you have go ahead some of the sensor grounds that we have are 50 millivolts if you’re off 143 millivolts with an inaccurate meter you’re not going to find a problem so that’s why I’m emphasizing that you need a point 1 percent or better accurate meter all right ok now you can test the accuracy of your meter if you if you have a scan tool that you use every day and you happen to have a GM vehicle in there check the oxygen sensor bias voltage it’s 450 millivolt check it with the scan tool and check it with your meter now if if you don’t have go ahead if you don’t have a scan tool you know some guys don’t up there then you’re just gonna have to find somebody that has an accurate meter that knows it’s accurate and test your meter against his that’s what I’ve done in the past ok all right well going on here to the next slide and that is the go ahead meter setup notice what a meter on the left want to click in ok we got that meter set for bolts and go ahead again and the meter on the right is set millivolt now if we had if we’re going to read a you know and want to read accurately and and what you anticipate reading initially is not critical if you set the meter at voltage or millivolts because if you’re at millivolts it’ll just say you’re over the limit if you go over 400 or 600 whatever the limit is you have to know that on your meter but I’m trying to show you what the route meters would read like if we were going to read 50 millivolts on each meter one set to voltage one set to millivolts go ahead okay 50 millivolts on the meter on the left is going to read point oh five volt that means 50 millivolt go ahead and 50 millivolts as read on a ammeter that set to millivolts we’ll just read 50 okay a lot of guys get confused by this alright and if you’re over the highest value on a on a meter set to millivolt it’s just going to say oh well no damage is done to the meters not analog anymore and so you can just move it from millivolts to volts if you’re over that you know over the range of your meter okay go ahead now the weird about meter selection okay I don’t I don’t push any brands of meters but I want you to take a look at the word fuse down here you see 10 app you see fused you see 300 million up you see fused okay as a meter you can buy go ahead next one here’s another meter set up you got 10 amp max fused you got 400 milliamp max fuse alright flip on the next one alright this is a meter I stay away from here you got on the amperage you have unfused amperage 20 amps for 15 second maximum what’s that mean well that means if you go over 20 amps for 15 seconds you’ll never you never use the amperage on that meter again it’s unfused and it’s unrepairable so that you better have something Lucas smoke still Steph you got it but it just the point is if you haven’t bought a meter and you’re going to buy a meter make sure every circuit on there is fused because it’s much cheaper to replace the fuse than it is to replace the meter makes that you I mean I mean today we’re working on on highly complex electrical circuits but and and this is a professional tool I mean yeah if you’re just doing yourself and you’re playing with your own car in the driveway and you’re trying to figure out why your headlights don’t work don’t go down to Manny Moe and Jack and get you a cheap tool to do the job if you’re trying to make a living though you’ll finding problems in today’s electronic circuits invest in the tool it’s going to last I’ve had my multimeter for at least 10 years and it served me absolutely well so that’s an excellent point and I know in classes that I taught I’ve had guys bring meters to class and I was somewhat astonished by what’s out there there’s a lot of stuff being used that is not accurate and if you’re going to try to do voltage drop testing you absolutely have to have an accurate meter however there’s a next slide okay now this one is okay this is about voltage drop testing and how to do it where do you start okay a lot of guys pass up the post and the cable go ahead this is a very simple test this is where you want to start you put the and it doesn’t matter that we’ll talk about this later folders drop testing is not polarity sensitive unless you’re using min Max and we’ll bring that up later but here I’ve got the positive terminal positive probe I’m sorry of my my meter touching the cable and the negative probe is touching the post of a post type setup engine cranking I don’t want to read more than 100 millivolts maximum allowable voltage drop across that this is this will trip you up a lot this if you don’t troubleshoot the post first you’re going to have trouble that’s for sure go ahead with the second one next one okay now what about a side mount let’s go on the next slide here I say oh I don’t have a batteries got a post on I got a side mount that’s that same slide I showed before electrolysis is waiting to happen go ahead click on there you should remove that clean it and reinstall it as a starting point to good effective voltage drop testing any side mount battery if you got a problem you think you got a voltage drop problem on the vehicle I would pull that off clean it put it back on and then start doing your testing or you could get tripped up as a result of having a problem at the post itself thank you all right so now we cleared both positive negative post or if it’s the side mount we’ve cleaned them put them back on the very first step after that is to check and see what is my source voltage and we call that open circuit voltage test you’re testing the battery state of charge that’s all it is this is a standard charge has been around for a long time and hasn’t changed I’ve got you can see my meters on here this has twelve point six three that tells me if looking at this chart this battery is a hundred percent fully charged if I had 12.5 I’m at 75 percent and I had 75 percent yeah you probably wouldn’t take the time to charge the battery at twelve point five but if if I’m at twelve point four nine I got a problem okay I’m going to charge the battery probably do a load test on it before I get involved with voltage drop testing everybody got that I hope okay on alright now this is a after we’ve checked source voltage and let’s say let’s say that we check source voltage and we got we’ve only got 12 volts 12 point zero zero you got a problem on the vehicle you don’t want to do any boulders drop testing till you find out why the battery’s not fully charged maybe the battery sulfated maybe the alternator is not doing what it’s supposed to be doing you got to have a fully charged battery to do effective voltage drop testing once we got the fully charged battery we’re ready to go cool then it I have up here on this slide the easy 3 step if you take a look at number 1 that’s my checking my source voltage at the battery okay now notice that the the positive post or the positive probe of the voltmeter now going back about oh I think I think I got ahead of here but let me see if I can yeah it’s just a click back that’s good back there we go thank you okay and the number one setting with your positive probe is at the battery positive and start off to do this in a very simple method is just put your negative probe on the negative side of the battery and leave it there clip it on there once you clear the post though the first step is what’s source voltage if it’s fully charged or 12.5 you’re ready to start testing now the load out here look at take a look at number 2 on this chart that’s could be any load on the vehicle this could be a light bulb via tail light could be an input to a control module any kind of load on the vehicle that position number 2 is going to tell you how much of that source foliage that exists across the battery is available through the input of that load at that point whether it’s it’s a hot all the time whether it’s hot with the key on or a hot and hot with the key and run or start or whatever the situation happens to be I don’t know third step of the easy 3 step it’s just checking the ground you’re on the ground side of any load on there it might be and if you have a control module you’ve got four grounds you got to check all four of those okay you can’t just get by with one they have redundant ground so they don’t run a whole lot of current through any particular solid state inside the module alright so this is the easy three-step I called step one what is source voltage step two how much of that is available to the input of any load on the vehicle and step three how much is being dropped on the ground side okay and we help at the end of this will have some charge for you which will sell you tell you what to expect out here okay so what I said we’re going to check the feed side the feed side the voltage eight died which is a positive side of the battery there’s two different values that are possible with your probe placement okay number one the value of source voltage available what does that mean how much of soaps voltage across the battery is available to the input of the load and that that’s one one of the ways that we can check there’s two different values possible by probe placement that’s what we’re looking at second the second one is the actual amount of source voltage that is dropped as two different ways now and this confuses people two different ways to find voltage drop one how much of the source folders across the battery is setting at the input to any load on the vehicle or two what’s the actual voltage drop from the pot inside the battery to the input of any load on the vehicle okay and we’ll do this go ahead we’ll do this by using a simple starter motor this could be any load but this makes for a very clear picture negative side of the voltmeter is at the negative side of the battery positive side of the voltmeter in this case our load is the Sardo motor so I’m at the input to the starter motor after the solenoid okay and we this will tell us how much voltage is available to the end for the load once we start cranking we want to see within two and a bolts source voltage on any starter today go ahead okay now I like this method myself go ahead this shows this shows the shows the actual amount of voltage that is dropped and what did I do well I took the I took the negative side of my voltmeter my negative probe and I put it on the input to the starter motor after the solenoid and I put my positive probe on the positive side of the battery and what does it bolt me to do it does nothing more than tell you the difference in voltage it sees between its probes so if there’s any voltage drop happening between that positive side of the battery and the input to the starter motor while you’re cranking of course it’s going to show up here this dystocia the actual amount go ahead and that I like this because there’s no no math required yeah and we just kind of go back and reset everything for everybody there Joe because in the very meet I’m gonna back up one slide for a second run in and I want to point out next in on the first test guys you’re hooking up your meter across the current path as joe describes it like you would if you were dredging it across the battery you’ve got the negative lead on the negative post the positive lead on the positive side of the load no matter what that load might be right you set it up that way you’re reading the potential between the two leads is joe explained that should be the same as the source voltage you measure that the battery right no if it’s what if there’s a difference that’s what you have to do the math yourself to figure out what the drop is but as just pointing out here by simply moving your meter placement so that you’re checking either end of that section of the current path you’re losing the meter do the math for you right now you’re going to get a much smaller number you’re going to get something because their it currents flowing there’s going to be some voltage drop right and in the if it’s a starter order I wouldn’t want to see more than two and I have volts on my meter right and but that but I’m saying is right and I want this is really what kind of screws guys up but they see what the meters saying they don’t understand what it’s telling them and what I want to make sure you understand here is that let’s just say that we have one here that has the maximum two and a half voltage drop while the engine is being cranked if the meter leads were in the first position instead of reading twelve six set the load while cranking you’d read ten point one right you have to do the math yourself okay by moving the leads over to either end of the current path is shown here you’re going to actually see that two point five you’re going to be the meters doing the math for you so right you want to make sure you know where your leads are and I also want to point out here that notice that Joe’s got one lead right at the battery and the other right at the load so he’s checking the entire current path now a lot of guys out there who are watching have got experience with voltage drop you know they can go across the connector or a section of wiring to find the drop that’s all fine and dandy if you’re that comfortable with the meters telling you but if you’re checking sections of that current path you’re going to miss something I always like to try to keep one lead reference to battery voltage we go to the battery itself right that’s a good point at what to what what’s come up in classes is well my leaves aren’t that long well it doesn’t matter I always suggest you get a 20 foot length a number 10 10 gauge wire you could actually use any wire because there’s there’s no significant voltage drop in the wire when you’re doing this type of testing okay all right so now we’re we’re looking at checking the ground side and this is just having the negative probe of the volt meter at the negative side of the battery positive probe of the volt meter on the ground side of any load and the meter then is set to millivolts it could be set to volts but millivolts because generally you’re not going to see more than 100 millivolts and if it’s a sensor ground you don’t want to see more than 50 millivolts so you can most meters will check in the millivolt range up to 400 millivolts so it’s still a little more accurate okay on the ground side let’s go on finder here I’m checking the ground side on a starter motor I’m on the starter motor housing neck either side of my meters on the negative side of the battery and the positive side of my meter is on a starter housing a note I don’t know if you can see in the picture but always scratch down and get the bare metal I don’t want the corrosion or the rust or anything to interrupt with my my accurate reading usually you can get rid of that stuff you can just scratch it off of there and for this test with the engine cranking 800 millivolts is the maximum now where do we get these numbers I don’t make this stuff up it’s actually a full chart by the Society of Automotive Engineers that make up the type of expected voltage drops and acceptable voltage drops that are allowable for any component on the on the vehicle you know there’s a chart like that you can get off my website ooh I do help go read it we do have a good good question here good about voltage of the battery and cranking the engine of course that’s going to drop as you’re as you’re cranking the engine that was just a good reason to use the second method that we showed you or Joe showed you by placing one end of the meter on the positive post and one end to the positive side of the starter because that since it’s doing them the math anyway it doesn’t matter source voltage changes right that’s fun right then the same thing with charging systems if you’re trying to troubleshoot a charging system that’s causing the you know lights to flicker event your if you go directly from one in the current path to the other and you let the meter do the math for you you’re going to see that varying difference all the time you’re not going to have to go back and try to do the math so Tom I hope that answered your question for you and Joe I’ll let you get back to us okay uh did he did he get the answer I mean is oh yes okay okay all right well now we’re talking about 800 millivolt max on on a starter motor when you’re cranking on the ground side because why is it higher than 50 millivolt on the sensor because there’s a tremendous amount of current going through here the higher the current the higher the voltage drop always okay all right now let’s go on the next one here and okay yeah this this is a 800 millivolt maximum and I’ve got a statement here what a difference 300 millivolts can make on on a I call them a shared shared current path which we’ll get into later on I’ll go ahead okay now we’re here I’m on the Block I’m not on the my meters not set up to checking the starter housing it’s checking the voltage drop between the negative side of the battery and the block and there’s a allowable for that that’s 500 millivolts or half full engine cranking this is a test of the shared current patch want to click on there again okay this is just another test and these are these are all explained in my in the book that we mentioned earlier you know if you’re looking for some help that had the vehicle there are a lot of guys that have written me and talked to me and they say that they they find it very useful because I’d use a lot of illustrations in here okay now I want to talk about 300 you know I said 300 millivolts is a is a large amount okay let’s stay there I want to give you an actual case that occurred this is from one of my classes I had here okay the this is what to get the kid told me okay I should say kid who he was a little bit older than a kid but I’m old so he was a kid all right car came in with the charge light on open circuit battery showed less than 12 volts so the battery was charge then it was load tested and it failed the load test so now this is him talking here he replaced the alternator the battery and the belt were replaced he just said seemed like the thing to do okay a week later car came back the same problem oh boy you know how that is all right and he thought the alternator was the problem so another new alternator was installed and he the vehicle was released again the next day same problem car came in the charge light was on so he said he then started checking the system and found no problems he said all wires in the system had continuity well continuity is not a good way to test we’ll deal with that sometime later he says his belt deflection was good the charge light came on at idle and was off with with any acceleration so this is what interested me he said he finally did a voltage drop test from the battery negative to the block and that says Illustrated on this screen here and he found that he had 800 millivolt drop now look at the look at the limit it’s 500 he had 800 it’s only 300 millivolts doesn’t seem like a lot of voltage at all okay but that’s what the society of automotive engineers say is the allowable voltage drop between battery negative and the block so he then cleaned the battery negative cable to post connection and that’s where we started tonight that’s where we started and he also playing the connection between the grounding point and if you look on there under the word block that’s the bolt that’s attached to the block here on this slide this fixed his whole problem the cars not been back never came back in for this problem again okay now what he did is he he was he tested shared chart paths for voltage drop and found a problem okay sure current path is another thing I talked to to Pete about we made Iran will get involved in that but you just cannot overlook battery cable connections and ground cable connections to the block that can drive you crazy okay all right Pete thank you I so this once deals with using the correct probe placement okay I’ve got a fuse box a switch and some kind of a load here all right go ahead okay now you can see where my probes are I met I’m at the tail end of a fuse in fuse box and I’m at the input to some load and all I’m going to check here go ahead click it on there all I’m going to check here is if you can see all those little blue arrows the only thing I can check with this setup is any voltage that’s dropping remember what a voltmeter reads now it reads the difference in voltage between its pros look what my probes are ones that of detail of a fuse and one is at the input to a load go ahead and want to click on again all right now this is an excellent uh it’s an excellent for finding a voltage drop of a switch contact okay I guess I got ahead of your one here I’m sorry go on back one win okay yeah you want to go back to the to these prior I think what something didn’t come up here okay huh okay all right okay thank you all right yeah this is an excellent a probe position for finding a faulty switch and if you had more than 300 millivolts on your meter that switch contact is pitted and corroded and you need to change the switch okay and in any switch any mechanical switch contact 300 millivolts is the maximum allowable on vehicle okay go ahead I know not to if you take a look now you can see where we were we were at the fuse and now I’m at the battery positive instead of being at the fuse but I’m also at the input to the load this is what we call the all inclusive test this makes the most effective use of your time you want it whenever you’re doing voltage drop testing that’s why I always want to go back to the battery and that this checks everything in there if you had a loose battery cable it would check it right here if you had a fuse that was loose an inline fuse or maxi fuse or a fuse box fuse for that circuit or the switch itself any resistance caused by corrosion or looseness remember airspace okay it’s going to show up here the all-inclusive test is what you should start with to do the most effective voltage drop testing okay all right you go back to what Joe is showing you earlier with the 1 2 3 method this is step 2 right right okay now that this has always come up in classes and I’ve had and actually when I was first working I worked for General Motors for quite a while and Pontiac in their manuals that they would direct you to a unplug the load let me tell you a story that happened to had a kid in Grand Rapids and he worked for a dealership he study Bovada came in and it had a digital dash that did not work and so he he went to the manual and looks up digital dash does not work so he starts following manual says unplug the connector to the digital dash so he did it says check for voltage available on pin 16 I’ll just make up a PIN number pin 16 he had source voltage it said check for continuity to ground on pin 4 some ground wire somewhere and he checked it it had continuity to ground and so it said replaced digital – he did order the new – puts it in plugged it in doesn’t work calls up the tech line people they said did you do check for a boulder they all he did was ask him what what the book said he said I did all that stuff he’s telling me the story they sent out a field engineer came out to the dealership these are the guys that if the dealer can’t fix it these guys get involved and fix it and guess what he did he left the connector plugged in and he did a voltage drop test on the feed side he had voltage he did a bullish drop test on the ground side he had source voltage it was a piece of wire that the ground wire was hanging by one thread continuity Tigran never tells you it has to go to carry current so he got stung by unplugging the load and I don’t advise doing this and a lot of manuals tell you to do that that’s the way to test and let me show you why it doesn’t work okay next slide all right this is this is the digital dish you see the light bulb on there that’s the kids digital – it’s working across the battery right now I’ve got got a connector on one side of the battery I’ve got the light bulb which is a load which could be any load on the vehicle including a digital dash and a bravada which isn’t around anymore I guess okay next slide source voltage on this vehicle was twelve point five nine volt okay next slide now look what I’ve done here I’ve left the digital – the load the light bulb plugged into the positive side of the battery I’ve unplugged the negative side that was thought wired kept the thing running and I put in nine hundred ohms of resistance in series with this load and look at my voltage its source voltage this confuses people okay its source voltage how can that be go ahead it’s this it’s this simple fact resistance any amount of resistance has no effect on voltage unless current is flowing current has to be flowing you cannot have a voltage drop of any kind without current flow my guys don’t quite grasp that and it’s important there will never be a voltage drop okay go ahead it’ll never be a voltage drop without current flow that’s why if we say you want to check the voltage drop on the starter motor you got to crank the starter motor you want to check the voltage drop on the input to a electronic control module you got to make sure that that module whatever it operates is trying to operate it okay all right next one okay this is a setup and procedure there’s a chart for this looking for parasitic load this this has been on the net for a while and I’ve had this on my website for a while go ahead if you want to find the if there’s a parasitic load on the vehicle there’s a simple test just checking the voltage drop across the fuses if the vehicles are off everything’s shut off all the lights are off the doors are closed etc and you’ve got the maybe you got the hood up and you got that light unplugged because you don’t want that load there shouldn’t be any current traveling through any fuses except the fuses that are cheap in the electronic control module alive okay if you if you check across the fuse and that fuse is not involved with the memory of a computer I say that fuse operates I don’t know make up something up fuel pump or something you know you got a voltage drop across the fuse that operates a fuel pump when everything is shut off you got a problem alright so you can find parasitic drain parasitic load if you want to call it by checking the voltage drop across fuses and the setup and the procedure and the chart are available on my website okay alright we’re kind of winding down covered most of the things I want to cover on voltage drop I this this little chart here when the low voltage is the same as source voltage it’s going to happen to you in your troubleshooting it may up happen to you already okay let’s take a look at the next one I’ve got a source voltage in there Joe oh go ahead let’s take a hair of some minor issues here all right so the guys can see better all right yeah I apologize for the temporary setback there fellas again this is the beauty of doing things know doing things live ma I’m impressed that it’s gone this well this far really it’s good for a second here okay sure honey jump across the screen again back to my okay booth and okay you go we’re on to the next slide alright now this is source my source here is 14-6 this engines running okay and let’s say go ahead I go out I go out I want to check the the how much voltage is available to the vehicle or or how much bullies in the I’m sorry to the starter motor or any other load on the vehicle if I see exactly the same as source voltage fourteen point six no drop whatsoever then there is no current flowing you’ve got an open circuit somewhere okay this tricks some people up sometimes and that I bring it I just bring it up because it comes up in class classes all the time guys having a hard time dealing with this if you see the same as source voltage then there’s no current flow I guarantee you when there’s current flowing you will never see exactly the same as source voltage at the battery because of airspace in the current path is going to drop some boulders and that’s the maintenance pressure that’s required we talked about earlier okay thank you okay alright here’s another thing is uh you’ve done all the work you’ve found the voltage drop problem and you’ve made the repair and the voltage drop is still excessive so where do you go from here go ahead the only answer here that I found in my experience is that some component in the current path that you’ve repaired is probably a parallel circuit some component is drawing excessive current and what way I work with it is if say there are three or four things on in this same current path that are all in parallel and I’m working with one I find a problem and I go back and I check again and I still got a problem there’s some other component that’s in parallel with the component you’re working with that’s drawing your sex of current and the way you find it then is to determine how many loads are on this fuse or on this in line or whatever it is you’re checking in that current path and you have to start with the key off of course now unplug something and retest and unplug the third thing or the second thing and retest you will find the problem but when you have a repair is done and the voltage drop is still excessive something in the current path that you’re testing is drawing excessive current it could be a short – internal short not a short to ground for dead short but an internal start where the windings have been bypassed and it’s drawing a little more excessive current you may want to keep that in mind okay all right next one all right this is just I’m at them I’m at the tail end of a little truck that I own and I’m just checking on some things and that black lead is going up to the negative side of the battery I’m looking for voltage available to the load back here I’ve got it I use a 20 foot piece of 10 gauge wire with alligator clips on it now you could use 22 gauge wire because there’s not going to be any current flowing because the meter has 10 million ohms of impedance in it there’s not going to be any current flowing so it doesn’t matter what gauge wire I just suggest 10 gauge because you can use it for checking 20 amp because if you want to use it as an amp you know a lead protesting amperage also but that’s how you get from front of the vehicle back to the taillights is self a piece of wire make it up you know if you’re working on trailers and 53-foot trailers and get a 53-foot piece of wire you know there’d be no voltage drop because of the impedance of the meter any questions on that are we doing all right check their tube Joe that you know a lot of guys use the power probe okay that that those leads are usually long enough to to reach all the way back to one of the car the other excellent has a ground connection there so if you have one in your box you can use that too we do have some comments on the the point you just made about excessive current draw in a component if that drop is except if you have a problem the component does still show up once you’ve done your three three steps you mean if if the if if there’s a I don’t quite get the question go ahead well if they if they let’s just say the component does indeed have excessive resistance okay okay would that that was that’s not going to show up in step two the voltage is getting to that that point but what do you think you’d see when you moved it to the to the other side if you move into the ground side your your think about where your probes are you’re going to be between the the positive side of the battery and the and the ground side you’re going to pick up any voltage drop occurring on the ground side if you have excessive resistance in a motor you could be across the motor now what here’s what here’s what should happen if you had if you have available voltage to the motor let’s say you got a charging voltage of fourteen two and you’re operating a fuel pump of some kind you’re checking the voltage drop on on the input side to the fuel pump okay y’all have within a bolt and a half of source voltage to the input if you have that you still got to check the ground side if you check the ground side and you don’t have an excessive voltage drop on the ground and you’ve got a we’re talking about a motor that has high resistance okay at that point I think I’m going to go just directly across the motor and see what’s what kind of voltage drop I’m getting across the input and the ground side children order that that’s another way that you can test you know and if you test on number two is good and your test and number three is good and the circuits not working the way it should it’s got to be whatever was in between test point two and test point three yeah and that’s a good point in that and I think later on down here I got some size on load testing you know get get the component out of the picture and test the wires we’ll take a look at that okay I’ll go ahead here yeah mine now a word about voltage drop testing polarity you want to click on give me two quickly sir holy drug testing oh no I’m sorry I I thought I had it on I guess it’s not on your slide want to back up okay yeah there you go all right okay a voltage drop testing is not polarity sensitive the meter on the left I’m I’m across positive my positive probe is on the on the left side of this load and my negative probe is on the right side my polarity is correct and I’m reading thirteen point four three charging goals okay and the picture on the bottom notice it’s the negative sign there I reversed my leads I still get an accurate reading it just tells my meters telling me how your your polarity of your meter is not hooked up in sync with the polarity of the battery now it doesn’t matter unless you’re using a meter that has min max if you want the minimum to show in the minimum window and the maximum that the meter picked up during your test to show in the maximum window and you got to have correct polarity just be aware that I got stung on that that’s why I know that okay been there done that okay here’s some ballpark you can just yeah half a volt maximum between the battery positive and most low current load inputs a bold and a half maximum between battery positive most high current load input the difference between low current and high current is high current are a run with relays low currents or not okay 200 millivolt max for any wire or cable 300 millivolt maximum for any switch contact 100 millivolt max for a load ground and 50 millivolt max sensor and computer ground now I didn’t make these up these are these are standard acceptable voltage drop of setup by the Society of Automotive Engineers the guys that design these vehicles they know what what you can do okay and these are available on my website also under testing and troubleshooting okay the next one next slide deals with kind of like the problem the the motor that has excessive resistance or someone asked the question this is a company’s our computer plugins to a computer on a vehicle that I was working on and I didn’t know if I had a bad box or not so all I’m doing here is I unplugged the computer key off never ever unplug anything or plug anything in today on any vehicle with the key on okay there are some exceptions but I’m not going to tell you what they are because just don’t do it keep the key off when you plug in or unplug anything interval just not worth it you can smoke something ok I here I’ve unplugged a computer and I’m my black wire is heading back to the battery negative and I plugged in to the positive one of the positive voltage feed wires to this computer and I got an 11 50 light bulb in there so now the light bulb is my computer what am i doing I’m load testing the voltage feed wires from to this computer all the way back to the battery negative and that light lights up now I don’t go by how how bright lights are I will actually put my meter on and see what’s the voltage available there now all this things under low if you follow me okay same thing on the ground side here my red lead is gone back to the battery positive terminal and my black lead it from the light bulb is plugged into the ground from one of the ground I think this computers got about four grounds on it and I’m all I’m doing is checking the wired if you got a module unplugged and it’s sitting on the bench you can’t smoke it if you plug in lightbulbs into the wires that feed voltage to it or the feed ground of four or from it we should say okay load testing you know voltage drop testing is just one another tool in your box don’t forget load testing you suspect a bad box or a bad module or a bad motor unplug the motor load test the feed wires to it and the ground wires away from it if they’re working fine and and the whatever it was you unplugged is not working it’s got to be bad okay all right that’s on the ground side and that’s just about all I’ve got it’s for a meter okay well I’m going to tell you something else too guys it’s no secret that cars are moving I look to more and more electronics I mean it’s just everything in the car eventually is going to be electronic that’s just the way it is and and if you’re the guy that that gets ahold of this voltage drop testing method you understand the fundamentals you work at it you make it yours then you’re going to be the guy that gets to get that money and it’s clean work run charge of premium because there are people out there that just can’t do it you know so if you can be that guy if you can be the one who can handle those those kind of problems then that’s that’s certainly going to look good on your resume and you can make some money absolutely to point out that hey you go on look him up on Facebook for some of the Demeter leaves of the amazing see how he did it yes this area soldered a well what am I going to repeat it for you guys see it on the chat window just check them out Jim thanks so much for the tips and you know with that we’re running really low on time I gotta say good night to Joe okay and I gotta say good night to you guys I really want to thank you all for coming out tonight look for us again second day for Tuesday for after-hours going Joe thanks again and thank you very much again have a great night really appreciate it okay have a great evening Oh


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