How many circuits for a wiring harness for an much older car?

I used a Ron Francis wiring harness on a car. Very high quality but a bit pricey. If you go to their website there is a questions/answers section in the catalog that answers a lot of questions about how many circuits you really need and also things to plan for. 

I robbed an ABS sub panel and all the wiring I  could easily strip once for a race car. I do not remember the make of car but I went to the wrecker and poked around for one with enough circuits. It got me a bunch of fuses and relays and was pretty much free. Lots of cars have one panel inside and one smaller under the hood. Probable on the order of $10.00 instead of hundreds.

Keith Tanner said:

Driver development isn't vintage? Are you only allowed to let your wife run a stopwatch with a clipboard? 

Sensor inputs into the ECU aren't usually run through a fuse, but the feed to those sensors probably is. You will definitely need a feed for your injectors, and it's your call whether that's on the same circuit as the ECU or not - if one loses power, it's probably not important that the other one continue to function. I'd get the wiring diagram for that ECU or the whole car if you're cutting down a production harness and make a list of all your circuits. That was the first thing I did when I rewired my Land Rover, a list of all the circuits cross-checked against the need. And I threw some extras in there, such as auxiliary lights in case I ever wanted to run them - such as your laptop or camera power. If you ever run at night (I've seen vintage night races, I know they're real) you'll want to provide power for lighting for those mechanical gauges. And what if you want a shift light? What about a rain light? Is that tied to the wiper circuit? Or is rain not historically accurate? ;)

I have no doubt a fair number of vintage racers do the driver development thing.  I'm equally sure it helps. 
    As for me until I can find a really accurate sundial. And maybe some stone tablets to chisel on I ain't a gonna bother.;-) 

   Honestly,  I'm not that serious about winning or whatever.  It's just going to be  one last run in the sun.  
 I want to hear that V12 scream down those long straights.   Maybe find someone to dice with. 
    The typical front runner will have more in his last engine rebuild than I'll have in the whole car.   The only gaskets I'll need are the cam cover gaskets to replace the stock cams with a pair of cheap regrinds.   The rest of the engine will be straight out of the junkyard, untouched. 
      Power wise I might approach 600 horsepower with very skinny legs.   Other than minor ( cheap) suspension mods  everything there will remain stock.  If I can find a pair of R calipers I'll use those otherwise it's Wilwoods 

Oh, I have a few suspension tricks up my sleeve but they are pretty generic.     Jaguar did a nice job on that geometry and I have to be careful not to lose that.  Trade the soft Quiet ride for precision.  The front will drop a bit.  

GameboyRMH said:

Keith Tanner said:

What about a rain light? Is that tied to the wiper circuit? Or is rain not historically accurate? ;)

Modern rain could be historically improbable

Well I'm such a sweet old Geezer that I'm afraid if I go out in the rain I'll melt. (you know sugar?;-). 

bearmtnmartin (Forum Supporter) said:

I robbed an ABS sub panel and all the wiring I  could easily strip once for a race car. I do not remember the make of car but I went to the wrecker and poked around for one with enough circuits. It got me a bunch of fuses and relays and was pretty much free. Lots of cars have one panel inside and one smaller under the hood. Probable on the order of $10.00 instead of hundreds.

I really like that approach.  Except I'd like to find circuit breakers  instead of fuses.  That way maybe I can reset it and get back to the pits rather than waiting for the tow truck.  

In reply to bearmtnmartin (Forum Supporter) :

That's a good suggestion, and 2nd gen Rams have an under hood panel on the driver side fender with fuses, relays, and circuit breakers that could be a good starting point. 

Is your turn signal switch OK ?

many of  1970s  VW switches  have problems now being made of plastic which gets brittle and snaps , 

not sure what the work around is as the replacement ones seem to be trash.

I used a 14-circuit cabin-mounted harness(1 relay for the horn)....as well as a 6-circuit engine-bay mounted PDC with both relays and fuses for those 6 circuits. its enough to run everything needed on a DOHC v6 with Ti-VCT with all the supporting things(fuel pump, injectors, ECU). No matter how you do it though I don't think you will be able to build a truly modern wiring system without an engine bay mounted PDC(unless you want to run extra wire length just to hide the PDC somewhere else)

No Time said:

In reply to bearmtnmartin (Forum Supporter) :

That's a good suggestion, and 2nd gen Rams have an under hood panel on the driver side fender with fuses, relays, and circuit breakers that could be a good starting point. 

That MAY be a computer module and not just a dumb fuse/relay box.

I have also repaired many Chrysler relay boxes with external relays when the internal ones kick the bucket.  Heck, CHRYSLER has repair kits and instructions for this.

In reply to Pete. (l33t FS) :

That's definitely a possibility, I haven't had to dig into one far enough to see if there's more going on than just power distribution, but I believe the ECU is on the firewall.