Accessory Fuse Block and Cable Install in a 4WD – How to add 12v accessories to your vehicle

Accessory Fuse Block and Cable Install in a 4WD – How to add 12v accessories to your vehicle


so if you want to install a secondary
fuse block this is what you’ll basically
need I’ve got some six b&s cable I’ve
chosen 6b&s for a specific reason
which I’ll talk about later and most
importantly I also have a circuit
breaker which is put between the battery
and this cable so in the event of
electrical fault somewhere along this
cable length this shuts off and stops a
fire after that I’ve got a STfuse
block holder then of course various
connectors grommets and shrink wrap and
then the lighter duty cable for running
to my accessories such as this 12 volt
socket so let’s get into the
installation for your fuse block i’d
recommend something like this st fuse
block holder this one comes with the
negative bus which i’d recommend as it
allows you to trace all your earths back
to the one single source which is your
12-volt battery so your main cable lead
will come here connect to this the positive
connects to this it reduces any chance
of reliability issues being introduced
from poor earths if you try earthing to
the chassis in various points something
like a defender for instance with
corrosion in different areas dissimilar
metals cause aluminium corrosion old
rust dirt in between panels it reduces
the effectiveness of the earthing system
but by running all the earth back to one
place then you reduce or minimize
completely that reliability issue from
poor Earth’s plus all the fuses are in
one place and can be labeled and easily
found these are made in six and twelve
block fuse holders so this time I
opted just for a six fuse holder as I
don’t need much more but should ever
want to upgrade I can pull this out swap
it over to the 12 fuse variety and I’m
good to go again
I found a spot in the back end in my
rear storage box where I’m going to
install the fuse block it’s a fairly
protected spot so I know it’s safe and
it’s easy to get to if I have a blown
fuse
another thing to consider for your
wiring to ensure reliability is to make
sure you don’t have any places where
you’ve drilled a hole and run a wire
through that is bare steel it’s using
this scrap steel as an example if a wire
went through a hole it would sit on the
bare steel and over millions of
corrugations it would sit there rubbing
and rubbing and rubbing until eventually
the insulation rubs through and it
earths to your bodywork which could
cause a fire or at least many blown
fuses so to stop this from happening you
should always use rubber grommets these
basically run the cable through it so
you’re protecting any holes in your
firewall or any bodywork panels you’ve
ran wires through and this now protects
the wire so it’s bouncing around and
protected by insulation another
possibility is to use split tubing if
you’re running a wire on the outside of
the vehicle this is a simple way of
running it into the split tubing through
in the inside
as you see there it’s nicely protected
so that could also be used if running
through a wall a hole in the in the
bodywork just again making sure you have
a reliable electrical system which isn’t
gotta start a fire when you’re in the
middle of nowhere. The following section
is a general guide for entertainment
purposes only. Consult an auto
electrician for your particular needs.
So let’s look now at the two cables I’ve
chosen this is six b&s cable it has a
thirteen point five millimeter square
cross-section of copper and has a maximum
carrying capacity of eighty two point
four amps at thirty degrees Celsius this
one is six millimeter auto cable and
it’s 11 b&s approximately it is a
four point five millimeter square
cross-section of copper and has a
maximum of thirty eight amps so to work
out which cable is good for what we need
to take into consideration the
voltage drop so there are three ways of
calculating voltage drop for your system
there are formulas you can use which I
have two here to show you as an
example there are tables online plenty
available online Just do a quick search
for 12 volt voltage drop calculator
or table and there are apps available as
well such as on your smartphone or as
free calculators online so there’s
plenty of ways to do it if you don’t
want to work out the maths itself let’s
look here at a couple of these formulas
which you can work out so voltage drop
equals amps by the total length of a
positive and minus so if it takes three
meters to run to the battery to the fuse
block then it’s three meters of
positive and three meters of negative
totaling six meters You times that by the
resistance the ohms per meter which you
can get from the manufacturers website
so in this case six b&s I made a
theoretical 50 amp carrying capacity
just in case I want to add a anderson
plug in the back end in the future and
run maybe a small inverter for 240
electricity or if I buy a secondary
fridge which might take another six amps
or so to run or any future additions I
want to make sure that I never have to
upgrade this again so 50 amps by 6
meters at the two lengths times the
resistance equals point four two volt
voltage drop which works out three point
five percent loss so three point five
percent is between three and four
percent which is about the maximum you
want in the 12 volt system so 6 b&s
for my particular cable run here of 3
meters from the battery to the fuse
block is excellent this will be plenty
for all future additions in reality I’m
only drawing twelve point five maximum
now with all my current accessories so
assuming I do get a second fridge or a
little camp oven or something crazy like
that then we’ll say 20 amps of a maximum
current draw by the six meters by the
resistance equals 0.16 volt or 1.4
percent loss so this is more than
capable of running a highly efficient
electrical system to my
fuse block without any real power loss
let’s look at the six millimeter auto
eleven b&s. this is running from the fuse
block out to the accessories the most
I’d ever draw through a 12 volt
cigarette lighter adapter it’d be about
10 amps a laptop is currently the
greatest draw I have which is at a 8
amps so assuming a 10 amps for a bit of
leeway 10 amps by the 8 meters by
resistance equals 0.33 volts or 2.7
percent loss so again this is below the
three percent recommended maximum so
this is also quite sufficient of
carrying 10 amps the 4 meters with less
than 3% voltage drop which makes
quite an effective reliable system
another calculation you can get if you
do not have the ohms per meter or ohms
per kilometer manufacturer’s numbers is
to use this formula down here voltage
drop equals a total length of the
positive and minus times the amps you
want the cable to carry times point zero
one seven which is a standard rating for
resistance of copper divide that by the
copper cross-section in millimeters
squared which you get up here such as
six millimeter Auto is four point five
millimeter square you can get that from
tables online if you don’t know the
exact number that works out down here
to 0.30 volt voltage drop which works out
very similar to the 0.33 volts of 2.7%
again using either formula I’m well
within a safe range for voltage drop for
this particular sized cable for the
length that I wanted to carry and the
current it must transport so hopefully
that’s a bit of a rundown of why I’ve
chosen these particular cables another
thing to note too is I also chose to get
fully sheathed dual core positive and
negative in a single wire that
just adds an extra layer of protection
on the outside to protect the wire from
chafing I also chose marine tinned
copper cable which is a
higher spec for marine environments good
for when it’s getting near water such as
a Defender going through water crossings
as this cable will be running on the
outside of the vehicle down below along
the bottom chassis rail so it’s just one
extra level of protection to ensure a
long-term reliable system not necessary
but I was happy to spend the extra few
dollars to get tinned copper wire I
found a spot I’m going to run my cables
unfortunately there’s a lot of wiring
there already so rather than trying to
force the cable through the grommets
already in place I’ll drill a new hole
put a new grommet in and that way it
keeps everything separate and there’s
less chance of wires chafing and rubbing
together or contacting bare steel and
rubbing through the insulation
and there’s two of my finished cables
one end has Spade terminals for the
12-volt sockets and the other end ring
terminals for the fuse block
everything’s crimped heat-shrinked so
there’s very little chance of any
moisture getting into the cable and
causing corrosion down the track this
cable should give me many years of
reliable service in the outback when
running cables on the outside of the
vehicle I like to add split tubing just
as an extra layer of protection although
this cable does come in its own
protective sheath it’s just one extra
layer which protects against heat for
example if it comes close to the exhaust
or from any other stones or chips or
potentially even rats or mice out in the
bush climbing in and having a nibble
which I’ve had happen before all the
connections were completed with the
battery and the fuse block wired up I
added a cover over the socket
connections for protection on the
passenger side I have a 12 volt socket
and a dual USB charger and the driver
side to 12 volt sockets the fuse box
also powers all the lights in the
backend I also did something crazy and
bought myself a 12 volt oven.
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30 Replies to “Accessory Fuse Block and Cable Install in a 4WD – How to add 12v accessories to your vehicle”

  1. Very helpfull video for anyone doing their own elec work, as well as pointing out the mandatory through bulkhead use of grommets. It was a little funny as well when seeing the botchy older wires coming up next to the new work you were doing, I know this was older work probably not done by yourself but would have been a good "what not to do example" anyway mate good video as always.

  2. Looking at setting up a dual battery in the 110. I have most of the wiring sorted on paper, however having not done this before a bit lost on the starter/Aux battery isolation wiring setup. As I understand th purpose it to isolate the starter battery to maintain starting capability whist the Aux/Acc battery can be discharged etc… I have acquired a projects DC/DC unit to manage this … all good here. Where i am lost is actually how to isolate Acc power. On the Defender there is power to IGN which is is used for both starter primary and accessories, so how does one isolate AUX power with only one connection for power to IGN?

  3. Can't you buy charts to calculate wire gauges. Because listening to your calculations gave me an almighty headache .lol

  4. A handy tip to weather seal your exterior cables is to use conduit/tubing but NOT the split variety, get the un-cut tubing instead, fully sealed. Run the tubing the full length of the wiring to the terminals at each end and use 'glue-lined' heatshrink to cover the tubing and the terminal so all that's exposed is the ring/lug/spade terminal at each end. Provided you melted the heatshrink long enough for the glue to work and you covered any holes on the terminals (some are sealed, some are not) you have a super long lasting cable that won't corrode after many many years. Very good video πŸ™‚ Always informative πŸ™‚

  5. It’s always good doing a bit of wiring and then benefiting from the installation. I bet down the track you will find something more to add. Bravo from Victoria Australia

  6. Hey I'm planning of setting up some 12v sockets and usb sockets up on the backboard of my tray (trayback ute) from my second battery with this same fuse box and wiring but the box and wires are going to be on the outside of my car (inbetween backboard of tray and the cab)… will they be okay outside of the car? They wont be easily knocked or hit or anything but will be exposed to the weather and dirt….

  7. What a Easy-to-Follow, thoughtful video. I wish other people kept the viewer in mind as much as you did when you made this.

  8. Felt like I was more in a math class than watching someone install wires and doing electrical stuff. Did not see any install segment, just clips of the already finished product.

  9. Excellent video but one minor word of advice. Buy a professional quality crimping tool (i.e. with ratchet action and die type jaws). For a long time I used an amateur crimping tool and had periodic problems with terminals loosening under vibration. I have had no problems since buying the professional tool (I carry the simple crimping tool for repairs on the road). A further tip – buy a tool wth interchangeabl dies because you will occasionally encounter uninsulated terminals (esp. on Japanese equipment) which require a tighter bite.
    It's an excellent idea to use heat shrink sheathing at the terminals since iit acts as a bend restrictor and reduces the chance of flexural failure. This is essential for any cables attached to the engine which will fail otherwise.
    The common earth is a great idea for a new installation. If you are dealing with an old installation with local earths (as on my old bus) the best tip is to use star washers with silicone compound or grease to prevent oxidation of the contact area.
    Keep up the good work.

  10. Thanks alot brett, very thoroughly spoken and easy to understand im goin to run basically the same system i think πŸ€”

    just wondering for all your accessory sockets what size fuses did you run on each input? (Eg 10a for 12v socket, 20a for fridge etc?)

  11. 10:54 It looks like the insulation is starting to tear away from where the cable joins the far socket.

  12. That's a badass Land Rover. Wish they were as easy to come by here in the states. I'd pick one up in a New York minute.

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