Electrical problem I need to solve

I'm writing about an electrical accident that caused a few lighting wires to severely overheat and one wire burned completely through. The car is a 1960 Sprite. I'm not much educated about auto wiring and want to learn from forum members. The wiring was damaged when my Dad mistakenly turned on the Ignition Switch and the Lighting Switch on the Sprite (with a fresh battery); and then, walked away for a couple hours or so. I am wondering if the damage that happened when the switch was left on fits with what you would expect could happen because of turning on (and leaving on) the Ignition Switch and Lighting Switch with a new battery (and a partially installed new wiring harness).

The car had recently had a brand-new wiring harness installed (following a carpet fire in the cockpit area that severely damaged all of the under-dash wiring). Only a limited number of wires in the new wiring harness were connected -- these included the wires needed to start the engine and the wires to the lights in the rear end of the car. All of the other lighting wires in the front of the car and in the cockpit were disconnected, plus wires for accessories were disconnected.

The car was being re-restored when the carpet fire occurred; and then, the wires that accidentally burned by turning on the ignition and leaving it on was a second (and much milder) wiring accident.
The wires that were damaged severely when the Ignition Switch was left on include one of two (all Red) lighting wires that originate from one connection point on the Ignition Switch. In other words, these are the two (Red) lighting wires that are attached to one screw-on connector on the Ignition Switch. One of these wires goes through the firewall and it was burned bad enough to sever the wire (near the Ignition Switch).

(The other Red lighting wire that connects to the Ignition Switch seems OK, with only some superficial damage to the plastic covering of the wire, where it was lying along next to the wire that burned up. That [unburned] wire [with damage to its plastic covering] supplies the small light bulbs of the Panel. Those Panel lighting wires were all disconnected when the damage occurred. Also, the switch for those lights was completely off the car when the damage occurred.)

The Red lighting wire that burned in two makes a junction under the hood and divides to go two directions, with one Red lighting wire going forward to the lights on the hood; and, the other Red lighting wire going back through the firewall, all the way back to the lights on the back of the car.

(The Red lighting wire that goes forward to the front of the hood appears to have no damage to it. None of the lights on the front of the car are connected to wiring when the Ignition Switch was left on.)

The right-hand tail-light had three wires connected to it; and, at that tail-light fixture, it has some damaged plastic covering on the Red lighting supply wire. The wiring for that tail-light is grounded. (The pieces of Red supply wire going to the left-hand tail-light and the Red wire to the license-plate light [which I have been told doesn’t have a fuse] appear to be fine.)

Do these findings (a severely damaged Red lighting wire that goes forward from the Ignition Switch and then through the firewall, and, a mildly damaged Red lighting wire that goes backward through the firewall and all the way back to the right-hand tail-light) fit with what damage you would have expected to happen by leaving on the Ignition Switch with a new battery? For example, would you have predicted damage to some other wires? Would you have expected the worst damage to be near the Ignition Switch?

Thanks.

Hi there and welcome. I am writing this not near my car - and more to the point not near my wiring diagrams but, a couple of thoughts.

1. Original wiring harnesses tended to be on the thin side which is to say they could have been a thicker gauge - but, "saving pennies". I use my original harness (and had to repair a wire or two) but use relays on my headlights.

2. You mention a replacement harness - is it from a reputable company? The reason I ask is because I do not believe that red wires ever went to the headlights or the taillights. IIRC the only red wires I have are to interior (dash) lights. Head/tail lights should be green or green with a tracer colour.

3. Were the ignition wires hooked up to the starter or ??? (you mention the lights weren't connected) could the ends have been touching each other or something else to cause resistance while the switch was on? This would account for the wires heating up.

4. This has happened twice now - can I suggest that you ONLY leave the battery connected when you want to check a circuit and disconnect it immediately every other time. This is the voice of experience BTW. Another thought would be to use a 9 volt battery or to install a fuse at the battery which will blow before the wiring burns.

5. Wiring is not that hard but, do you have a wiring diagram and do you understand the standard wiring codes of British cars - Brown is hot unfused, unswitched, green on switched, fused etc. etc.

I think <think> if you repair the wires and add relays you should <should> be good to go. That said - welcome and keep the questions coming.

I always use a inline fuse holder that you can get at any auto parts place to fuse the whole system till you are sure you have it right. Use a hose clamp to clamp it to a battery post and the regular battery clamp bolt to attach to the cable. The whole system is then fused. Use a 10 amp to test everything except the lights. Recommend relays as well and a good wiring diagram. I would guess a short somewhere in the system.

Kurt.

Me again - the short in my harness was under the dash under the harness cover - what you might have experiences is actually from the first episode but unnoticed or unseen - two sires melted together. You might have to either uncover the whole harness or, at the very least check for continuity everywhere before you proceed.

Looking at the factory manual wiring diagram the red wires go from S&T on the ignition switch to the front side lights and rear tail lights.
The front and rear turn signals are green with red (left) and green with white (right), and brake lights are green with purple. Dash/instrument lights are red with white. I just rewired my Bugeye and this is how it is wired.


The front side lights and rear tail lights come on with the light switch in the H and S positions. The rest of harness that goes through the switch is hot when you turn on the key so yes, I would expect you cook the harness by leaving the headlight switch and ignition on since only some of the wires were connected and you don't know what the exposed wires are laying against and what was grounded and what wasn't.


I've rewired a few Bugeyes and always leave the battery disconnected and the keys out of the car until the entire harness is installed and then we go system by system checking that everything is working correctly.


Without splitting the harness open and inspecting each wire it's hard to say how much damage was caused by this. For safety I would chuck out the burned harness and start with a new fresh harness. That is far cheaper than thinking you fixed all the burned wires, missing one, and burning your car to the ground.

It's very unlikely you could burn up the harness by just leaving things on. Most likely is that there was a short somewhere. I'd take a good look at your combo ignition/lighting switch. Since many connections are stew terminals, you need to be very careful about stray strands making contact in places they shouldn't. Also, given that the old original switches can make poor contact as a result of corrosion of the contacts, a lot of heat can be generated through high resistance. It would be a good idea to add relays to high amp items like light and horns. Relays will take the heavy current load off the switches. You'll need to add additional wiring, but it's not difficult to do.

I'd also add a battery cutoff switch to the battery; easy to install and quick to disconnect/connect.

Thanks a lot for taking time to respond to my long Sprite wiring question. You have given me some good new ideas for how to solve my problem. Also, you have given a lot of good advice on how to protect my wiring from damage in the future.

This is a problem that occurred a number of years ago (work and family and other things kept me from attacking it until now). I'm not certain that the Ignition Switch was secured in its opening on the Panel. Maybe it was left hanging off of the Panel (suspended there by the various wires that connect to it). Maybe the S&T wire could have been allowed to be touching the metal of the Panel! Perhaps, if the S&T connection was touching the Panel, that could have caused a hot short when the Ignition Switch and the Light Switch were accidentally left on for an hour or two? (The battery was brand-new.)

Thanks again for your help. You folks are spread around the continent! The location nearest to my home in Kansas City (for the four folks who wrote replies) is South Dakota. Peace.

When I bought my my BE the DPO had run a screw into the wiring at the dash panel switch and the electrics were fried. That's when I devised the inline fuse idea. it wasn't easy to see. Some burned insulation that I later repaired but not much because the contacts in the light switch had let go first.

Good luck and I hope the damage isn't too bad.

Kurt.