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Car body loom and circuits

EFI Wiring Fundamentals

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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Hi guys,

I know this is an efi page and I know it's probably more basic knowledge but I thought I'd ask.

As part of my project celica gt4 the wiring needs to be addressed, I've got my head round most of the engine wiring and will be making an attempt to build a new engine loom very soon.

When I changed my dash over on the car I couldn't help but notice the dash loom and body loom had been hacked in to quite poorly as part of a bad alarm install and it got me thinking about binning the whole loom and making a new basic body loom to run the lights/brake lights, gauge cluster and fuel pump especially as toyota have relays all over the place so would be a good opportunity to have a tidy up.

Can anyone point me in the direction of some reading material or even diagrams of the circuits needed to make up a body loom before I convince myself to not bother lol.

Building body harnesses for a car you're going to use on the street (so retains heater, ac, power windows, mirrors etc) can get pretty in depth pretty quickly... Its a really old book, but still quite relevant, Haynes 4251, Electrical and electronic systems has some really great info in there and is quite well laid out.

Hi zac,

Thanks once again for the reply, the car will be pretty much stripped right down ac is already gone power mirrors stopped working probably 15+ years ago lol.

My main aim is to have it functioning the minimum requirement to drive it to track days so mainly just lights(indicators hazard head and brakes), wipers, horn and the dash

I will order that book thanks,


Your factory workshop manual with the original wiring diagrams and wire colors will be your best source of information. I would suggest you could repair the "hacked" harness far easier and end up with a more reliable product.

It's certainly possible to create a harness that would have the bare minimum needed for road-worthyness (MOT over there?) You'll need to spend a lot of time with your nose in the factory service manual for your car to determine the pinouts of all the switches and such, and how they operate.

My suggestion is to buy a used harness for your car. You will save plenty of time and money. Keep the old one for educational purposes, how it is build,why this wire goes there etc etc ..

I think I'm best just repairing the stock body harness and just making the new engine loom.

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