Thread from 2017:
Contemplating a replacement engine wiring harness on my lemons / chump, carb'ed 1st gen RX7. Basically just need wiring to the starter, alternator, distributor, coils - at least I think that is it... Never done this before so any advice is appreciated or links to a cheap option. thanks.
You got it.. just get some toggle switches for power and a push button for the starter..
Are you sure you don't want/need a few gauges as well?
FWIW, Painless has a ready-made kit for this: Painless Wiring Race car wiring Download the PDF manual and take a look at the wiring diagram. The kit price isn't cheap at $241 MSRP, but you should be able to duplicate it for less.
That said, wiring a car with all of the same color (or some non-standard color) wiring just to save a few $ will likely bite you in the middle of a race.
Del City and make your own on the cheap.
Ian F wrote: That said, wiring a car with all of the same color (or some non-standard color) wiring just to save a few $ will likely bite you in the middle of a race.
+eleven
When I made my MegaSquirt harness, I bought several lengths in different colors from wireandsupply.com. They've got different solid colors as well as striped wires. In addition to the wires I knew I needed, I also pushed a few extra wires through the firewall so that as I added projects, the wiring was already in place. I did eventually swap that out for a DIYAutoTune MS harness when I upgraded to MS2, though, but during the time that I ran my homemade harness, I had no problems tracing wires. There is a ton of truth in making sure you run different colors for each function along with documentation of those colors. I keep a binder with the car that has (among other things) not only the MS wire colors decoded, but also decodes what's left of the factory wiring harness. There are two copies of the list, one sorted by primary wire color and one sorted by function.
I built one for my first gen RX7. You can use the factory gauges by hooking up power, ground, and single wires from temp, oil pressure, and the tach signal. Gas gauge is one wire as well.
You need a switch/relay for the fuel pump and power to the ignition and a button for the starter. That's the sum of what the car needs to run. It's pleasantly simple. You're likely to need a master kill for a racecar, so build that into your plan as well.
Do you need front lights? Rear lights are another switch for running lights and utilizing the stock brake switch for brake lights.
None of it is hard, but you need to take your time and label the ever living crap out of everything.
I'm only looking to do this on the engine wiring since it is a mess. I'm not looking to wire the entire car.
As for gauges, the stock water temp is basically an on/off switch so don't need the stock gauge or wiring for that. I'll go aftermarket. The oil pressure is useful and so is the tach but I already have aftermarket gauges for those so don't need them either. The gas gauge is useful and already works so I'll keep that too.
I saw that painless kit but it is more than what I paid for the car 
Hoping to find a cheaper option.
Anyone have a how-to for engine wiring harness?
amg_rx7 wrote: Anyone have a how-to for engine wiring harness?
Well... get a wiring diagram, modify it to suite your needs, loosely connect the dots with wires, zip tie the wires together and to the chassis, trim the excess and add connectors. Add more zip ties to neaten things up (figure every 4" or so - yeah, you'll go through a lot of zip-ties); plug in the connectors. Where wires may rub against something, wrap in harness tape.
Having rewired a car, there isn't really a good "how to" since every car will be a bit different depending on what you want. You'll make mistakes and learn from them. There are a few things I did that I will try not to do again. The big mistake I made was to install the connectors before doing the final routing and trimming, especially under/behind the dash, so the wiring there is a rats nest.
If you can, follow the factory routing as much as possible. It was probably routed that way for a reason and deviations will likely be regretted. Plus, most cars (at least the older cars I've worked on) have welded belt tabs to hold the harness to the body.
Oh - and expect the project to take a LOT longer than you think it will.
Someone can correct me if I'm wrong, but from what I remember......the ignition coils need power. The distributor talks to them over the included ignition wires, so all it really needs is power to the coils and once you turn it over it fires. One wire to the coils. Done. The alternator has one wire, mine ran through the kill switch so....check your wiring diagram but I think this wire should be switched and come on with ignition. Then fuel pump. That's it on the engine side for a carbed 12a. Feed power to the coils, alternator and fuel pump and they'll run. Starter is push button. That's it. Honest.
I've used multi core cable when doing wiring looms for trailers and also lighting systems for industrial machinery quite successfully. I've always thought it'd be an easy button for doing a basic engine harness, though probably a bit more wasteful. The only real draw back is you'll need multiple earth's, so you'll still need to splice the earth wire multiple times.
On a 1st Gen RX-7, depending on which distributor is used, the ignitors need power and ground as well. 1979 & 1980 used points, but 1981-1985 had an electronic ignition and the wiring is a bit different.
In reply to mazdeuce:
"Easy button" is to buy the Painless harness - at $241 that's only a few hours of your time to replicate.
Zombie thread, canoe deleted
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