Wiring is one of the big jobs that quite a lot of otherwise-handy DIY or hobby mechanics shy away from. And I reckon it is because people are lazy and just want a quick fix – this was certainly the case for me!
Maybe it is the fact you’re presented with dozens (or hundreds in some cases) of brightly coloured wires? You can’t see the electricity flowing through all those wires, and wiring diagrams would give even a Buddhist monk cause to swear, so handing electrical work off to someone else is totally understandable.
But it is also lazy.
With the wiring nightmare under my dashboard causing me serious grief I consulted a couple of auto-electrician friends and their advice was dire – even though I’d had a custom wiring loom put in my car I was better off ripping the under-dash section out and starting again.
This sent me into a flat spin as I hated the idea of wiring, let alone redoing a car’s loom! Thankfully, I’ve made a good start on the job just by being logical and methodical, writing down steps, dummying my work up, then checking with my professional mates (and Dr Google).
Having wired my Haltech Elite 950 ECU into my car I had some confidence to tackle this job. I mean, I’d wired ignition coils, a crank sensor, electric fuel pump, and injectors on my own so how hard could this job be?!
I have gone through some of the basics of wiring an ECU into a classic car on this website with my Ultimate Guide To EFI:
The Ultimate Guide To EFI pt1
The Ultimate Guide To EFI pt7
The most important part of doing this job is patience, and not being afraid to stop and research or ask questions.
The first step to sorting this issue out is to get a notepad, a Sharpie, and some good quality masking tape. You’ll be unpicking wires from the fusebox, marking them and reorganising them into something much neater.
Once I had untangled a bunch of these wires I was able to actually see where the installer had gone wrong. While it could have been fixed with a bunch of time and effort, I chose to cut out much of the loom.
I purchased a whole new 21-circuit wiring loom from Bluewire Automotive as they sell GM-style reproduction kits. I got a 21-circuit kit (THIS ONE) even though it was overkill for my needs. I am going to reuse the wiring in the car as much as possible, but move where the fuse box sits to behind the stock glovebox door (as I can’t fit a glovebox now the Vintage Air Magnum evaporator lives in that spot).
Now, I will admit right here that I don’t have anything resembling a perfect understanding of auto electrics. I rely on my friendship with much smarter people than myself who do, and the number one piece of advice I would give anyone wanting to do auto electrical work is to find someone who understands this field and doesn’t mind you asking a million silly questions. Because you will, and sometimes you’ll mess up. That’s life, guys.
Once I had the new wiring loom the first job was to sit down and read the instructions. Then read them again, making notes for important steps. I work on my car sporadically and that means I need to leave reminders, to-do lists, and the like for myself so I don’t redo things redundantly.
I laid the wiring loom out and actually went through the fuse box to work out what circuit I’d need for the body (things like headlights and horns), what I could reuse (central locking, thermo fans, stereo), and what I could get ride of (hazard lights, power windows).
I unpinned the circuits that weren’t required, thinning the fuse box out handily but leaving me the option to add circuits in the future if I decide I want to install power windows, a disco ball, or a soft serve ice cream machine.
Working out the circuits under the dash and organising this fusebox took a grand total of 3 days. Sometimes it was damn frustrating but then I think that comes back to it being fairly fiddly work and me having the patience of a hand grenade.
The image above shows the fuse box as it came (with the relay for the hazard lights already pulled out). The image below shows how easy it was to thin the fuse box down to only run the circuits I need.
I’m not going to run the thermo fan or electric fuel pump through this fuse box as the Haltech already has a fuse box which these can be wired directly into.
Here is the fuse box put aside until the car is painted. I’ll rewire it after the paint is down to save this mess of wires getting covered in body filler dust or over-spray. Each circuit has been loomed together with cable-ties to make them easier to identify, and I have done the same under the dash with clear labels on what each circuit is.
Get used to this. Trimming wires once they’ve been run and triple-checked to make sure they’re not short is key. You also don’t want to deal with too much length so I get the length right, then add another 2-inches.
This isn’t a small job, and you’ll need to invest some money in good-quality crimpers, cutters and wire-strippers, but spending good money on tools is never a bad idea. I’m also going to use a modern flexible braid as a sheathing agent on some parts of the loom, replacing the hard corrugated plastic split-tubing as the flexible braid is nicer looking, and has a lower profile.
As soon as the car is back from paint I’ll make a Part II to this post and show you the good, the bad, and the ugly for rewiring your body loom. And I’ll start with how to fix The Ugly…