A little advice from the builder brain trust...wiring a rod or race car

Assuming you are building a street rod or race car built on an existing production based vehicle. Say something like a C4 corvette. Further assume you eliminating many wiring intensive systems such as fuel injection, a/c, heater blowers, radio, interior lights, etc. All you really want to retain is taillights, brake lights, headlights, starter switch and ignition system.

Is it easier/cheaper to just start from scratch? Or do just begin paring down the stock harness? How do you approach this type of project?

Bit of the answer depends on you.

For about $150 you can get an aftermarket 15 circuit wiring harness. The wires are all marked along the lenght with their respective function

If you thin the harness, everything should plug in when you are done. You will be able to use the factory manual to troubleshoot.

In reply to Ovid_and_Flem:

Getting desperate on that weight shaving eh? I'd pair down the factory harness. Really you're keeping the lighting harness as factory but pairing down the engine harness. Carb right? You need alternator, starter, HEI, oil pressure, and temp right?

In reply to Ovid_and_Flem:

From what I've seen poking around on mine, the lighting circuits are separate from everything else once you get out from under the dash. I don't think it would be too difficult to pare off everything else.

In reply to Stampie:

LOL...No, not really a weight thing. More aesthetic than anything. Dash is out and I don't wanna look at a multI colored wire spaghetti mess.

I cleaned out the harness in my 3rd gen Camaro, it was easy to do, I removed the whole thing from the car, to make it easier. Just de-pin at the box, don't clip, in case you need to put something back or want to add a circuit for something else later.

If you really want to go lighter on some things, you can switch to LED bulbs, then the wire size can go down since they don't pull near the load an incandescent would.

In reply to NOHOME:

Yeah...Speedway has a 12 circuit budget harness ($150) designed for street rods for cars with minimal accessories but challenge budget may limit me from that option this year. Really curious of any first hand experience. Painless has budget systems but they're a little more pricey.

Ultimately after this year's challenge if I get running issues sorted my plans are to rebody the B&S C4 with an interesting body.

In reply to t25torx:

Depin??? English for a dummy like me

In reply to Ovid_and_Flem:

Remove the wire from the connector with the pin attached as opposed to just cutting the wire. Depinning allows you to put the wire back easier.

Ovid_and_Flem wrote: In reply to t25torx: Depin??? English for a dummy like me

lol de-pin... "As to remove by pushing back the metal pin or clip (usually with a tiny flathead or actual straight pin) holding the metal terminal in the fuse box"

In reply to Stampie:

Gotcha. One of problems with the old plastic piece of e36 m3 is that it seems to have an inordinate number of ancillary grounds.

I have done cars for others both ways and sometimes it's quicker one way or the other. While the list of items in the OP is just the basics knowing exactly what kind of car is being modified and if there's things that may have been forgotten but are necessary would help. Power windows? Door locks? Wipers? Currently have VAT? Will use original ignition switch?

In reply to NOT A TA:

C4 corvette that has been gutted. VAT has been disabled. Going to carb so no FI/ECU...just HEI Distributer.

Essentially just a vette kart.

I've wired from scratch, used kits and pared down factory harnesses. Pareing down the factory harness is the cheapest and can be the easiest way to get a factory look. Rolling your own from scratch is often the most expensive is pretty time consuming but when done well gives the best results both aesthetically and functionally. Universal kit is quick and reasonably priced. In the OPs case I'd probably pare down the factory harness.

In reply to APEowner:

There's definitely a lot of room...even though it a 30 y.o. car it had a lot of bells and whistles: power windows, power door locks, power antenna, 8 interior lights, 3Rd brake light, 2 underhood lights, electric cooling fan, aux cooling fan, VAT, fog lamps, stereo, yadadada. I almost don't know where to begin.

I'd say quicker to buy a cheap kit but cheaper to strip out the unnecessary if a challenge budget is a consideration. If it's a digital dash era one I'd get rid of that and go with regular gauges for water oil etc. If it's one of the earlier regular gauge ones you can keep them without having the computer leaving the original gauge wiring intact. Can you sell all the wire and electronics as scrap toward challenge budget?

As a practical matter, how do you recommend approaching a parING of stock harness? Do you start at component you're removing and work towards main fuse panel or vice versa?

In reply to Ovid_and_Flem:

Yes, I always do it that way. Then whenever you make a cut, check to make sure everything that you want to continue working actually does.

I am actually facing the same thing with the Molvo project. The minion is pushing for the aftermarket speedway harness, but I think the factory pared-down stuff is a better answer. My reasoning is that with the aftermarket, you have to re-do every single connector in the car on both ends. For example, I want to use the stalk controls on the finished car. If I keep the Miata harness, it is one big connector at the column. If I use a speedway harness, I have to create my own connector(s) for both sides.

If you can find OEM terminals for your application, it would be possible to de-pin the one side, crimp the terminal on the speedway wire and re-pin for a clean solution. I have not gone looking for who sells Miata connector/terminal components.

If this involves a challenge budget, the the pared-down OEM is really the correct answer in spirit and budget.

In reply to NOHOME:

When I rewired a Spitfire with an aftermarket harness, I reused the OE connectors at the column for the ignition, turn signals and wipers. Not a big deal. Just more soldering. IIRC, those were the only special connectors on the car. Everything else was either spade or bullet connectors, which I replaced with new.

For a Challenge car with budget restrictions, then paring down the OE harness would be the way. Just remove it intact from the car, tagging the ends as you go, then cut out what you don't need. If the car has a digital dash, It's likely you'll still have to make up a new harness for the replacement gauges, but you should have plenty of extra wire to do that.

Pete Gossett wrote: In reply to Ovid_and_Flem: Yes, I always do it that way. Then whenever you make a cut, check to make sure everything that you want to continue working actually does.

Dude....do you ever sleep? Posting after 2 a.m. then again at 6 a.m.

I'll thus forgive your ambiguous answer. So do you start at fuse block or component? Vice versa?

Plus I gotta figure out how to save ECU/FI section of harness to preserve system for someone.

In reply to Ovid_and_Flem:

That's what I get for posting with minimal sleep! I start at the end point and work backwards to the source(fuse box, ignition switch, battery/ground, etc.).

Ovid_and_Flem wrote: As a practical matter, how do you recommend approaching a parING of stock harness? Do you start at component you're removing and work towards main fuse panel or vice versa?

Here in FL we have no emissions inspections or testing so this has become somewhat common. Last one I did was a late 80's IROC clone that got a carbed SBC and T-400 swap.

Does the car have an original automatic in it? If so that's a consideration.

In reply to NOT A TA:

Yup...700r4 tranny

If you are just looking for the basic circuits, lights, horn, etc then by all means rip out the factory crap and wire it from scratch. It will be much less pain in the long run and you'll know exactly where everything is.