How to transform a rat’s nest of wiring into an orderly harness

By Carl Heideman
May 4, 2024 | electrical, Wiring, electronics, How To | Posted in Electronics & Electrical Systems , Features | From the May 2023 issue | Never miss an article

Photography by Carl Heideman

In the hierarchy of automotive dreads, rust repair and wiring rank near the top for most people. Rust repair we get, but wiring doesn’t have to be a nightmare. After all, a wire just goes from one place to another. How hard can that be?

The problem is there’s always more than one wire. And those wires connect to things. And …

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JG Pasterjak
JG Pasterjak Production/Art Director
3/24/23 11:00 a.m.


[narrator, watching me do wiring]: It turns out, he could not do any better than this.

gumby GRM+ Memberand Dork
3/24/23 11:12 a.m.

Both timely and appropriate as I prepare to make better the American Autowire harness in my own Type65.

Looking forward to the future installments, and thank you for sharing your knowledge and experience

Pete. (l33t FS)
Pete. (l33t FS) GRM+ Memberand MegaDork
3/24/23 1:18 p.m.
JG Pasterjak said:


[narrator, watching me do wiring]: It turns out, he could not do any better than this.

Thus the current Colin conundrum.  I want to do better than this.  It requires a crazy amount of planning, because wiring harnesses look like that when things are added after-the-fact.

The Dork
3/24/23 11:59 p.m.

I would welcome some tips on thining out  thee harness of my e36 track car, just want push button start, brake lights, fuel pump etc.... thanks in advance, the

Pete. (l33t FS)
Pete. (l33t FS) GRM+ Memberand MegaDork
3/25/23 12:59 a.m.

In reply to The :

The slow but sure way I have been doing it:  Identify a connector you do not need, cut the connector off of the wires, remove the loom (if it is like the R53, the loom is cloth tape wrappings) and resecure the harness with a few zipties at strategic points, extract the wiring from the loom by PUSHING to find where it wiggles.  Continue until you get to a splice (cut at splice), ground junction, fuse box, or wherever else it terminates.

You will need to re-snug the zip ties on occasion as you thin the herd.  That is why zip ties are nice.  Get big bag and be generous with their use.


Here's a pic I took while I was about a quarter of the way through my current progress.  Almost all of the wires running down the tunnel area are gone except for about seven or eight, for the power mirrors.  Likewise a lot of the ones on the right, quite a few on the left, and I even got it to the point where I was able to re-loom the wiring in spots.

The Dork
3/25/23 9:48 p.m.

Pete, thanks for the tip, thats kind of the way I was thinking, take out a wire, does the car still run, yes/no go or stay. thanks, the

DaleCarter GRM+ Memberand New Reader
3/26/23 1:40 a.m.

     The "physical" aspects of wiring... proper crimping, gauges, connectors, looming, routing, etc are great and this article is addressing that part of the job. Will you get into designing a wiring topography that isolates data circuits and their power supplies from the "noisy" side of the car that carries fan motors, ignition systems,e tc ? Also, proper grounding is crucial.

     I bought a Panoz GTS that had been a full-time race car for about 20 years and, along the way, "Race day" repairs had been made to the wiring harness. When I pulled the dash tins off, revealing a bit of a rat's nest, my coach and friend said, "You can just put that right back and walk away", but I knew I could never unsee that. The last thing I wanted on my mind at 165 MPH entering 10a at Road Atlanta was "Man, that wiring is a mess". :-)

      I rewired the entire car from the firewall to the rear bumper, removing old, broken circuits, adding a rain light, a new switch panel and all the "oddities" from two decades of repairs made under the time pressure of getting back into the race.

     Proper wiring, with proper devices and materials, gives me a real peace of mind on track, plus elevates my knowledge of the car.

russelljones48 New Reader
1/8/24 8:49 a.m.

I have created my own mess.  I wasn't happy with my FFR roadster set up as it came from Factory Five so I installed a good aftermarket generic 20 circuit harness.  I'm now trying to get that looking like the pics on the boards and not having any luck.  So, my fallback position is to sort bundle and remove the excess.  It's this last piece that is driving me nuts.  What to cut? where to cut? Should I be ruthless and eliminate wires that I could possibly need in the future...  ?#*#?*!?   HELP

Jesse Ransom
Jesse Ransom GRM+ Memberand MegaDork
5/17/24 6:41 p.m.

I don't suppose you guys have the order from your "kit" from Terminal Supply sitting around as an example BOM?

RacingComputers GRM+ Memberand Reader
5/18/24 5:52 p.m.

We have found that if you draw out what you want on a single piece of paper, then start removing what is not need in the harness, it goes rather wekk.



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