DIY | Multimeter basics for automotive use

DIY | Multimeter basics for automotive use


– Hi everybody.
I’m Matt Lewis with
Hagerty and in today’s DIY,
I’m gonna talk about the
basics of using a multimeter.
When you’re looking at multimeters,
there’s a lot of different options.
We’ve got very small pocket sized deals,
very expensive professional tools,
and then you can get in to
just the average multimeter.
This one here is great because it’s got
all of the options you’re gonna need
for checking the electrical
system on your automobile.
A little multimeter like this is
available in a lot of different places.
You can find them at hardware stores,
you can find them at auto part stores,
you can even find them at
home improvement stores
or anywhere online.
An item like this which is
great for the DIY home use,
$20-$25 it’s gonna do
almost everything you
need from a day to day usage.
Now that we have our multimeter open,
you can see there’s lots of
options as to what you can test
and actually, more
connections on the front
than there are leads that come with it.
We’re gonna be focusing on DC voltage,
ohms or resistance, and amperage.
Depending on what we’re testing,
we’re gonna be plugging the leans
into these different terminals.
We’ve only got one black terminal on here
so that’s obviously going
to be our ground lead.
First thing we’re gonna
be working with is voltage
so I’m gonna go ahead and plug it into
this one labeled voltage.
For the sake of testing voltage,
I’ve got a little battery
here hooked up to these leads.
Since there’s actually electricity
at the end of these leads,
I’ve put down some cardboard so
our metal table doesn’t start conducting.
With this multimeter,
there are multiple options for voltage.
What it does is it basically moves
the decimal point around here.
We know that cars are 12 to 15 volts
depending on the situation so our 20 volt
max setting is gonna be plenty for
what we’re working with
on the automobile here.
You can move it up to 200 which you
see just jumps this decimal point,
and even to 500 which
eliminates the decimal point.
While you gain head room for voltage,
you lose accuracy because you can’t
see portions of a volt
at the 500 volt setting.
At 20, we’re great.
We know we’re not gonna exceed 20 volts
and we get plenty of accuracy with
to the hundredths of a volt.
I am gonna warn you that electric cars
run super high voltage,
enough to be lethal.
If you have an electric or a hybrid,
I would advise just taking it to a shop.
Don’t mess around with the electrical
system on it because it is dangerous.
When you’re testing voltage on a car,
you’re gonna remember that this
black lead is going to be
your negative terminal.
That’s gonna be the ground.
We’re gonna go ahead and hook it
up to our pigtail here with the black.
This red one is gonna be
the positive terminal.
That, we’re gonna wanna
hook up to our positive.
Here we see, this little battery I
have is reading 13.81 volts.
That’s pretty normal for a 12 volt system
to actually read higher than 12 volts.
A regular car battery’s gonna be
between 12 and 13 if it’s functioning
properly with the car off.
When the car’s running, your
charging system kicks in,
you might see anywhere from 14 to 15 volts
depending on what your alternator or
generator is currently doing.
When we’re talking about voltage,
what we’re actually looking at is
the electrical charge difference
between the negative terminal of a battery
and the positive terminal
of a battery or a circuit.
A good analogy for that
is like water pressure.
When you’re looking at
the water in your home,
how much pressure does it have?
Next thing we’re gonna
talk about is amperage.
You can consider amperage
like the flow rate,
so how much water is actually
coming through the system.
For amperage, I am gonna have
to move this terminal over
from our voltage setting
to our amperage setting
just like this and I’m gonna have to
swing our dial over to
the DC 10 amps setting.
This is gonna allow us to measure
amperage instead of
voltage on this circuit.
When you go to measure
amperage on a circuit,
you do actually have to
disconnect the circuit
and put the multimeter in between
the power and the load
or light in this case.
I hooked up the red lead to the positive
and I’m gonna hook up the black lead
to our red lead here which will
complete our circuit
and turn the light on.
Pulling just over half of an amp.
We’ve tested the voltage of our battery,
we’ve tested the amperage of the circuit
with the light bulb on.
The final setting we’re gonna talk about
is this ohm or resistance setting.
What that is is it measures how difficult
it is for electricity to
pass through way circuit.
When we’re looking at a little
piece of wire like this,
this is just copper wire,
this should be almost zero
ohms or zero resistance meaning
it’s very easy for electricity
to flow through it.
If we go ahead and hook
our terminals up here,
once this settles we’re at .3 ohms.
This may just be a variance of
what the multimeter can read because
this is a fairly inexpensive multimeter.
It may be this does have a tiny
bit of resistance in it but,
basically we’re looking for a very
small number when you’re reading
something like just a piece of wire.
Right here I’ve got what
is an ignition coil,
I believe it’s off of a little motorcycle,
and measuring across these two points,
we’re gonna see how easy it is for
the electricity to flow from side to side.
We hook this up and we see
about five and a half ohms.
That’s more difficult for electricity
to flow than just this piece
of wire but, still fairly easy.
That’s not a lot of ohms.
For the sake of testing all three
things we’ve talked about today,
I’ve gone ahead and made
our light bulb broken.
This light doesn’t function anymore.
We hook power up to it.
There’s no light.
First thing we’ll test is voltage.
We’ve got our voltage set back up,
we’ll hook up to the negative terminal
and positive terminal.
Electricity is getting to
this point in the light bulb.
Next thing we’ll test is amperage to
see if that electricity is actually
flowing through the light bulb.
Go ahead and switch that over to amperage,
move our terminal over
to the amperage terminal,
and we remember we put the amperage
in line with our circuit.
Go ahead and hook this up.
It’s reading nothing.
I know that this circuit
is not completing,
meaning there’s something
wrong inside the bulb.
The final test we can do is our ohm test.
We’ll go ahead and move this back to ohms.
We’ll put our meter back on ohms.
We’ll go ahead and hook this
up and it appears to be open.
The meter didn’t even react.
What that means is there is nothing
connecting this wire and this wire
and that’s why the bulb’s not lighting up.
Now we know we’re gonna
need a new bulb in here
because the electricity can no longer
flow through it causing it to light.
We can replace this bulb and
just see if we can fix it.
For the sake of troubleshooting,
what we’re gonna do is we’re gonna
actually measure the
ohms of this light bulb.
The way you do this is these
bulbs, this is an 1157 bulb.
It’s super common for cars.
This outside ring here
is the negative terminal
and then what you have is
two positive terminals.
It’s called a dual filament bulb.
If you look really close you can see
there’s actually two filament sections.
Those are what produce the light.
We’re still on our ohm setting so
we’re gonna go ahead and
connect to the negative
and then probe this positive.
It didn’t even react when I hooked it up.
There could be a couple of issues.
These connectors here that
hook the socket to the bulb
might be corroded or broken,
this outside may no longer be grounding
properly to our negative terminal,
or really where these wires go in
may be broken or kind of anywhere
within this circuit it may be broken.
We grab a new bulb, we put it in.
Now we can use the same ohm
test, hook up to our terminals.
We’re seeing the numbers responding
which means electricity can
flow through this circuit now.
What that means is we have a good bulb
and a good housing with good wiring.
Now that we’ve fixed it,
if we hook our battery
up, we have light again.
If you find yourself with a brand new
multimeter that you want to play with,
you can do it with something as
simple as a double A battery.
Here we’ve got a positive
terminal labeled,
it says it’s gonna be 1.5 volts.
You can hook that up and play with that.
I hope this multimeter DIY was helpful.
If you have any comments or questions,
go ahead and post them below.
Make sure to subscribe to our channel
so you know whenever
we put out a new video
and we’ll see you next time.


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