Physical Wiring 

There are a few little tricks that make your wiring loom look a lot tidier and ease the job. Depending on how you want the finished loom to look I am a big fan of looming the individual wires together with thin cable ties and encasing engine bay wiring in ‘cobraflex’ split sheathing of suitable size. Insulation tape should be used as little as possible as it makes it difficult to trace wires or do alterations without removing it and ending up with sticky mess everywhere. If you are recreating the original loom use loom tape or self amalgamating tape (not insulation tape) to bind the wires.

Plan where the wires will run - and avoid exhausts! I prefer to wire from the dash outwards and terminate to length at the extremities. You can buy plugs in a variety of sizes that allow you to have joins in the wires. I am a big fan of being able to unplug the engine loom (especially with EFI) from under the dash and remove engine and loom complete without having to remove individual wires from instruments, fuses etc.

I wire a car in three ‘layers’, starting with the power feeds to the ignition and power sides of the fuses. It makes sense to loom this separately if you have the room. Next is the car side which comprises all the car systems excluding the engine. Again, loomed separately if you can, which is almost impossible in a Seven. Finally I wire the engine, ensuring it can be unplugged and removed as invariably you will have to remove it at some stage, and if you decide to upgrade the motor all you will have to do is change the wiring on the engine side of the plugs to suit the new engine.

It pays to check each circuit as you complete it otherwise you risk having lots of things not working and no idea where to start looking. If a fuse blows when you turn something on check the circuit, check your fuse calculations and see if you have the right fuse. Merely putting in bigger fuses until it stops blowing is asking for trouble.

Care should be taken to protect all panel penetrations with grommets sized as close to the wire as possible. I tightly wrap the wires in insulation tape until they are a good tight fit in the grommets. A dab of sealant is wise if you are really concerned with sealing out moisture, however, a little thought as to where penetrations will be made can result in the most being made of available shelter. If you are using standard EFI it makes sense to re-use the grommets fitted to the loom.

Mount all electrical devices where they are clear of drips from potential leaks (say from wiper post penetrations) or heater hoses if they terminate under the dash - I have had hoses leak. I had to drive through six inches of water once, which is a lot when you only have four inches of ground clearance, so keep things high up. Think about where stones and puddle splashes are likely to fly up, and keep clear of exhausts. Allow enough length for relative movement between engine and chassis. Also keep wires away from fans etc.

Conclusion 

Wiring a car can be done by the average enthusiast - but be warned it can soak up a considerable amount of time. Planning is crucial and drawing out the circuits first is a very wise move. It is normally possible to simplify circuits considerably from the initial design to the finished one. Try to amalgamate power feeds etc as much as possible to reduce the amount of wire in the car. Remember that one day you (or the next owner) will have to figure out how the wiring works so a problem can be fixed or an accessory added, so make a good diagram and stick to your colour coding.

We’ll make a Sparkie of you yet!