Wire size

[Edward Schubert]

What gauge wire should I use for my battery, starter button, on/off switch, rain light and kill switch?
Thanks

[SR Racing]

#4 is fine for your starter and battery. (you could #6 if runs are short.) Use welding wire, it is much more flexible.

For the primary ignition wire and solenoid I would use #12. #14-16 is fine for everything else.

Jim
SR

[Edward Schubert]

Thanks Jim, Ed

[hardingfv32-1]

Speaker or car audio wire is another option.

Brian

[craigs]

Along the same lines what amp size switches should I be using?

Main power switch on dash?
Powered from kill switch data logger switch?
Rain light switch?

Craig

[smsazzy]

You can run 18GA on everything except the battery to kill and starter run. I used 8 Guage on that. (If you run an O2 sensor, you might need slightly larger on that too - Maybe 12-14GA)

Most cars use grossly over-rated wire for our application.

Some people will tell you that is too small. I have never had an issue with it, and the person who helped me wire it restores vintage F1 cars for a living. I'll take anything he says as golden.

[fvracer27]

You can run 18GA on everything except the battery to kill and starter run. I used 8 Guage on that. (If you run an O2 sensor, you might need slightly larger on that too - Maybe 12-14GA)

Most cars use grossly over-rated wire for our application.

Some people will tell you that is too small. I have never had an issue with it, and the person who helped me wire it restores vintage F1 cars for a living. I'll take anything he says as golden.

I agree I have a friend that wires GT and GS cars and he told me that same thing everyone always uses way to much wire than what is needed.

Mark

[SR Racing]

You can run 18GA on everything except the battery to kill and starter run. I used 8 Guage on that..

You can run #22 wire if you want. However every wire size downward drops voltage at the load. (and is thus spread across the wire and at extremes can cause the insulation to melt) As the wire get hotter, its resistance goes up, dropping even more voltage and thus power. You would be hard pressed to tell the weight difference between 6ft of 18 vs. 14. Why not error on the side of safety? People are always woried about making sure they get every volt to the ignition system with good batteries etc. Why save .2 oz and 10 cents on wire when you give up that extra volt? (and arguably safety and wire insulation longevity. You wanna shrink on the rain light, go ahead. Not the ignition primary or batt cables (better cranking)

A primary ignition wire #16 will drop ~.2 volts+ at 8 feet. A #12 will drop ~.08. This doesn't consider the better surface area connection at your connector and the mechanical advantage.

Keep in mind that ONE wire size is ~1/2 the resitance (and thus current rating)

[racing stuff]

The universal formula/sport racer wiring kit we sell is made up of mostly 16 gauge wire.
The one problem with smaller gauge sizes, is their durability when it comes to any constant handling and vibration/loads from use.
A little larger wire gauge just gives you a bit of a cushion.

[SR Racing]

Keith. 16ga is fine for lamps and senders. A primary ignition circuit can easily draw 8 amps. 14ga is preferred and 12ga is even better. Never measured it but I suspect the starter solenoid current is close to that on a Vee. As you mention, mechanical issues are at play also.

If you look up recommended ratings 16A (eg) is workable for 8+ amps, however, that rating is for "free air" use. IE a wire running alone at 70 deg F. In a bundle it is rated far less and in temps at 100F to 150F it's a lot less. (Re: Primary ignition wire. WIth our low compression engines a primary voltage of 12.6 vs 12.3 isn't much, but why scrimp on a buck of wire?)

[racing stuff]

We have a 14 gauge wire in the kit of basically 16 gauge, for a heavy draw such as your ignition example. These kits have worked very well for years, maybe it has to do with the brand of wire. I've been told that differences do exist and that not all (?) gauge wire is the same.

[smsazzy]

We have a 14 gauge wire in the kit of basically 16 gauge, for a heavy draw such as your ignition example. These kits have worked very well for years, maybe it has to do with the brand of wire. I've been told that differences do exist and that not all (?) gauge wire is the same.

This is absolutely true. The impurities in the wire cause significant resistance.

[tiagosantos]

How about the other way around? Any disadvantages other than weight to a bigger than necessary wire?

I'm working hard to put on some weight, but since I'm redoing the harness anyway.. Could get rid of some lead and add copper! Might even add scrap value to the car.

[SR Racing]

How about the other way around? Any disadvantages other than weight to a bigger than necessary wire?

Nope. Well, unless you go as big as garden hose. Making small radius bends could be a problem.

[BLS]

While on the subject of wire (bigger is better ) , is there any reason not to run wire inside the chassis tubing? The only reason I can think of not to do it, is what happens in an accident when the tubing gets bent with the wiring getting pinched and shorted.

[smsazzy]

While on the subject of wire (bigger is better ) , is there any reason not to run wire inside the chassis tubing? The only reason I can think of not to do it, is what happens in an accident when the tubing gets bent with the wiring getting pinched and shorted.

Also it is difficult to secure. Since it is flopping around it is more subject to chaffing. Probably effects the next owner though. I gotta believe it takes a long time for that to happen. Although, it happened on my trailer brake wire that was run inside the frame in 4 years.

[FV80]

Barry,
From my perspective there are a couple of issues with running wires (and anything else) inside the tubes.
1). Your wire/whatever will be protected as much as possible inside - however, it will not be VISIBLE nor 'touchable'. That means, when you have a problem, troubleshooting it is TOUGH.
2). You might have to make a significant HOLE in the tubing for in/out - in addition to the wire, you SHOULD have some sort of rubber protection at entry/exit points - that means a pretty good size hole and that could cause significant loss of strength if you're not careful.

That's all I can think of at the moment. The strength issue, can be dealt with - the troubleshooting issue can only be dealt with (at the track) by completely replacing the entire length of whatever is in the tube (or pulling it out and inspecting it). I ran across an issue in an older Caracal not long ago - the throttle cable was run through the tube and had gotten gritty and rusty from years of use - it had WAY too much drag. The only solution was to pull it completely out and replace it. Not TOO big a deal and would have probably been the answer if the cable was NOT in the tube as well. For wiring, chaffing is the biggest culprit and could easily happen inside the tube where you can't see it - a bigger problem and not easy to diagnose I think. In my car, I put (most of) the wiring inside a PVC tube attached to the frame - similar situation, but the wires can't short to the tubing itself at least.

Steve, FV80

[fvracer27]

I watched a car almost go up in smoke because of the power wire running in the tube. The wire rubber on the tube (protective sleeve or groment must have moved) lot of smoke luckily nothing else caught fire while the driver was inside the car.

Mark

[BLS]

You make good points. I could deal with the chafing, entry/exit, and troubleshooting reasonably well. IF I were to run inside the tubing I would have the wire encased in an additional rubber tube for protection. I'm thinking of using my (design for now) 1.5 inch tube as the carrier and entry/exit is not an issue. However, I probably wouldn't do it this way, but it would make for a neater package if planned ahead of time.

Steve, I remembered your PVC tube from your build website and have thought about that as well. Seems like a reasonable way to do it.

Thanks,
Barry

[SR Racing]

, is there any reason not to run wire inside the chassis tubing? ....

People do it. I wouldn't. There is going to be a lot of vibration and thus chaffing of the wire potential. We run them out side with convoluted tubing for protection. And then it's easy to get to for repaitrs, etc.

Jim

[Dave33]

Something else to think about. If you're wiring your car make sure you have everything fused. My son bought his first vee last year and we didn't notice it was wired without a fuse panal. This is the result of several years different owners and wear and tear. Almost lost the car.
http://www.youtube.com/watch?v=FswpZQGPWHQ

[problemchild]

Most people do not want fo have a fusebox. If the car is freshly wired, and well-maintained, why would you? It increases the connections and potential problem areas by 200%. Cars with expensive electronics (like FF-Fit and FC-Zetec) do not apply.

[BLS]

I never used fuses on the old car and I don't know anyone that did. Since I'm an electrical eng, I do understand the need for them. One problem is the outdoor use, in the rain, a problem area for keeping connections and fuse panels dry. It is something to be considered.

[cendiv37]

I have used a small fuse "box" terminal block for years without problem, however I do not fuse the ignition. I can't remember if I fuse the oil pressure idiot lite sender either. probably not. I can finish the race with only these electrical functions operational. Everything else goes through a fuse. The "box" is a small block with maybe 4 slots for GM style push-in fuses. The fuses themselves are very small and durable and the connections have lots of contact, etc. The box is located behind the dash inside the bodywork and I've never seen that area get wet in my car, even when the rest is soaked.

If I were to run any wires through the frame (which I don't) I would DEFINITELY fuse them...

my $.02

PS: I'm a mechanical engineer and I don't understand electronics so I try to protect them as well as I can