How to wire a car from scratch

By Carl Heideman
Jan 13, 2024 | DIY, electrical, Wiring, electronics, How To | Posted in Electronics & Electrical Systems , Features | From the Aug. 2023 issue | Never miss an article

Photography by Carl Heideman

What do you do when you have to wire a car from scratch? Panic? Not so fast. Some methodical work plus proven techniques can easily deliver success. Yes, you can do this.

Our latest project, a vintage Formula Vee single-seater, needed a new harness, and premade replacements aren’t available. We had two choices: Buy a universal kit from companies like Ron …

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1. We started rewiring our Formula Vee race car by pulling out our old-school VW manual to find a wiring diagram for a 1970 VW Beetle. There are images of these diagrams all over the internet as well, but if you go that route, make sure it’s from a reliable source since many are not correct.

2. We built this spreadsheet to plan our harness, noting the color codes, sizes and routing of required wires. We also put part numbers of our switches and other components in the spreadsheet so we could get replacements when needed.

3, 4. We ordered our wire from Rhode Island Wiring Service and our German-style terminals from Goodspeed Motoring. (We’ll have a lot more details about wiring and terminal choices in an upcoming story, so stay tuned.)

5. We then installed our major components in the chassis, including the battery, voltage regulator, switch panel and more.

6. We started running wire with the largest one first. In this case, it’s the 2-gauge master battery wire.

7. We then started roughing the wires to and from the major components, starting at the starter in back.

8. By the time we got to the middle of the car, we had quite a mess on our hands.

9. So we started to neaten up the rough wiring in the back of the car and routed it through its final locations.

10, 11. We then repeated the process for the midsection of the car by roughing it out, neatening it and routing it.

12. There’s a lot going on in this picture as we performed one more neatening process. First, we were extremely fussy and made sure that the wires are routed parallel to each other in the harness and don’t cross each other. Note that we didn’t tape the harness or use other wraps unless harsh conditions would dictate extra protection. Zip ties keep the harness bundled neatly. Not only is this approach attractive, but it makes future diagnostics and repairs significantly easier.

13. We kept routing and neatening parts of the harness until it was done. Then we cut off the tails of the zip ties. We’re very careful to cut the tails with flush-cut snips so that we leave no sharp edges. Sharp zip tie edges can cause cuts severe enough to need stitches.

14. One more note about zip ties: We use them to bundle the harness or to secure the harness to the chassis, but not both. That way, if we need to remove the harness, we just cut the securing zip ties, allowing the harness to come out as a whole. A friend who worked on a Le Mans team taught us this “figure 8” method to secure the harness to the chassis: It puts a little space between the wires and the chassis, facilitating any future service work. It takes two zip ties to do this: a large one around the harness and chassis tube plus a small one between the harness and chassis tube.

15, 16. By following this playbook, we ended up with a harness that’s neat, easy to diagnose and extremely reliable for many races to come. We’ll cover more details and many more techniques in the next installment of this series.

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Comments

Tom1200 UberDork
6/14/23 5:09 p.m.

Is that the original location of the switch panel?

pmulry New Reader
7/27/23 3:45 p.m.

That "figure 8" method of securing the harness to the chassis is intriguing, but the photo doesn't make sense, probably since the tie wraps are all black so it's hard to see where the small one intersects the large one? I just can't figure how you'd do this with only 2 tie wraps....

paddygarcia GRM+ Memberand HalfDork
7/27/23 5:53 p.m.

Relevant 3rd grader joke: what did the zero say to the eight? Hey, nice belt!

Loop the large zip tie around the tube and wire, and leave kinda loose. There's the zero. Loop the small one around the large one, like a belt, between wire and tube. Draw the small one tight and voila, the zero becomes an eight.

Carl Heideman
7/27/23 6:10 p.m.

Tom1200 said:
Is that the original location of the switch panel?

I can't say for sure if it's the original location, but a number of Zinks have the switches there.

stylngle2003 GRM+ Memberand Reader
1/22/24 10:17 a.m.

pmulry said:
That "figure 8" method of securing the harness to the chassis is intriguing, but the photo doesn't make sense, probably since the tie wraps are all black so it's hard to see where the small one intersects the large one? I just can't figure how you'd do this with only 2 tie wraps....

Big one goes around the chassis and harness, but not fully tightened. Small one goes around the big one, between harness and chassis. Then I imagine there's some dance of tightening them both in steps until desired spacing/fit is achieved.

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