DIRTY STUFF

STREET machine electrics. Dark science to most DIY guys, but with a bit of know-how and straightout common sense, it is entirely possible to completely rewire any car, and save thousands of those hard-to-get dollar notes.

Firstly, you will need rolls of insulated wire, in 3, 4 and 6mm sizes and assorted colours depending on how many circuits you need to connect to, so you can easily identify the wire you want by its colour. Auto electric supply shops are the go for bulk wire and stuff like crimp-on terminals and heavy-bodied adhesive plastic tape. Where you need to run multiple wires, as in engine bay to rear lights, buy five- or sevencore trailer wire in 4mm. These multiple wires are already wrapped in black plastic, and are individually coloured.

A box-cutter knife will be handy to remove wire insulation, as will an electric soldering iron with a roll of fluxcored wire solder for making more reliable joints to terminals, plastic plug connectors and cable lugs used on the ends of battery cables.

A wiring diagram is essential, which can be found in most workshop manuals. With a bunch of lines connecting to strange symbols, it might look like a mad artist’s scribbling, but each wire and symbol is usually numbered, matching a list alongside the diagram that explains which bit means what. By patiently tracing out all these, that mess of lines and stuff will suddenly become clear!

Probably the most vital tool in your wiring arsenal is what I call a test pencil. This is a screwdriver-shaped, clear-plastic-handle thingo with a bulb inside, connected to a length of wire with an alligator-clip end, while

WITH A BIT OF KNOW-HOW AND STRAIGHT-OUT COMMON SENSE, IT IS ENTIRELY POSSIBLE TO COMPLETELY REWIRE ANY CAR

the screwdriver end finishes in a very sharp point. The purpose of this tool is for checking where the electricity is, by connecting the alligator clip to a known good earth – as in the shiny metal of a car body, which is almost always negative – and touching the pointy end of the tool on a wire connection or whatever. If an electricity supply is there, the bulb in the handle will suddenly light up. And why the sharp point? To shove through the plastic insulation of electrical wires so the point hits on the copper core. But as you normally hold the wire in your fingers to push the sharp point through the plastic, every so often it will slip and jab a finger; having lost a heap of blood over the years through testing wires, my massacred fingers will never be the same!

So all that is relatively simple. And car electrics get even simpler when you know that this mostly invisible stuff must always go around in a circle, from the positive terminal of a battery, to whatever component like lights or wipers or whatever, through a steel car body and then back to the negative terminal of that same battery. Otherwise the stuff will not work. And as street machine engines, transmissions and drivelines are normally insulated by rubber mountings, if you are using the body as the earth return, a short length of battery-sized cable will be needed to connect the engine or gearbox to the car frame so electricity will flow.

If you have installed the battery inside the boot, a really heavy piece of battery cable will have to run from there to the main terminal of the starter motor solenoid. The reason for this is that electricity travelling through a wire is a lot like water under pressure being pushed through a garden hose. The longer and thinner the hose, the greater the wall friction, which will really slow down the stuff until you get bugger-all at the end. Same with electricity: if the cable is too thin and long, electrical resistance will create a voltage drop. So in a battery-in-boot situation, a thin cable running all the way to the starter motor up front will result in the poor old starter barely cranking at all. From that cable connection at the starter solenoid, you will need to install a couple of what are known as fuseable links – short lengths of special wire designed to blow apart and shut down supply if you get a severe dead short. From these links, run a 6mm wire to the large output terminal of the alternator, and from there another to the main fusebox, which will serve as a junction point to run off positive wires to wherever they need to go as dictated by the lines of your wiring diagram. It is vital that every circuit, bar the battery feed to the starter motor, is protected by a fuse, whether it is one wire or half a dozen, as if you get a short in an electrical component, a wire will fry and set fire to your car!

It is quite okay to use pieces of the original car looms with their plug connectors, but it’s best to solder the wire joints and use heatshrink tubing to insulate. Don’t just twitch wires together and hope these will hold, as they will soon fall apart.

With some patience and practice, this black art will be a mystery no more!