This article was first published in 2004.
Head off to a wrecker and you’re sure to see some wiring looms sitting
around. Often they’ve been cut to get them out of the car and as a result, the
wrecker sees them as worth nearly nothing. For example, I’ve bought three large
looms in the last few months at AUD$10 each.
So what good are they then? Well, you can get a whole heap of good parts from
a wiring loom – let’s take a look.
If you’ve ever installed programmable management, an interceptor – or even
just wanted to feed a whole heap of new wires through the firewall – you’re sure
to have come up against the problem of sourcing an appropriate grommet. Off the
shelf hardware store items aren’t usually suitable because (a) they’re not big
enough and (b) they don’t have the ‘tail’ that makes proper firewall grommets
weatherproof. But in a typical wiring loom you’re sure to find one or two that
There are those that look like this...
...or larger oval-shaped ones like this.
Some looms even have firewall grommets that are backed by a metal plate that
bolts to the firewall.
Want to install an extra injector? Or swap an airflow meter? Often you’ll
find that sourcing the plug is the hardest part of the modification. But if you
pick a loom that’s from your make and model of car (or often any model from your
car’s manufacturer that was produced at about the same time) you’ll find the
right plugs in abundance.
This loom has ECU plugs....
...and an airflow meter plug.
You’ll also find two-pin plugs...
...and other two-pin plugs to suit injectors. In short, there’s plenty of plugs
of a myriad different designs!
Even if most of the components have been unplugged, many harnesses have
relays still attached. Because they come with a dedicated plug and a length of
cable, they’re easy to add to your car while still looking factory and
This relay comes with wiring, plug and bracket while...
...this design has a rubber shroud that can easily be mounted on a custom made
vertical bracket (it slides in where the arrow is).
And if you want a full relay board, try this out for size! Often the
individual relays and their dedicated holders can be removed – handy if you
don’t need a massive relay upgrade to the wring.
Dedicated fuse boxes can be found in nearly all discarded wiring looms.
Here’s how a fusebox salvaged from a loom was used in the installation of a
high-powered intercooler fan. The fusebox contains two high-current fusible
This fusebox is perfect for a general purpose upgrade – it has some fusible
links, fuses and a relay.
If you want to make new wiring look factory, you’ll need to use factory-style
fasteners to hold it in place. (This is so much nicer than just cable-tying it
to existing wiring!)
A variety of fasteners is used on looms – here the top one is designed to
clip into a drilled hole while the bottom attaches over the exposed thread of a
bolt. In both cases the loom is easily attached to the fastener with normal
This loom fastener comes with its own plated bracket.
This fastener is designed for a bulky loom and clips into a panel hole. It is
easily undone from the existing loom.
And don’t forget that when you buy an old wiring harness you’re also
acquiring a huge amount of useful insulated wire!
As can be seen here, there’s a wide variety of gauges, suitable from handling
heavy battery loads right through to wiring-in sensors.
Sometimes heavy duty lugs will already be crimped to the ends of the thickest
cables – very useful as getting a good crimp or solder connection can be
difficult on heavy-duty cables.
Bits and Pieces
And you’ll also find convoluted tube in a variety of sizes, multi-pin plugs
and sockets (used to connect parts of the loom), in-harness fusible links,
battery terminals – and a whole lot more.
If you can pick up a wiring loom for a few bucks – especially if it’s your
car’s make or model – do it. Put it to one side then when you need a fusebox, or
a relay socket, or even just a length of small diameter convoluted tubing or
some fasteners, dig it out. The on-car wiring job will look and work so much