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Re: electrical short wiring damage

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H

Handyman

Freshman Member
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Re: electrical short wiring damage

I’m writing to ask if others have had a wiring accident similar to mine and to ask how was the wiring harness evaluated and fixed.

My car is a 1960 Mk. I with an original, un-modified engine and wiring. My wiring accident occurred soon after a new Moss wiring harness was installed, while the car was being re-painted. Someone accidentally turned on the ignition switch (and apparently turned on the light switch, too), then walked away for several hours.

The taillight fixtures and license light fixture were connected to the wiring harness when the accident happened, but they did not have bulbs in them. The lights in the front of the car were not connected to the wiring harness. (Most wires under the hood, and the panel lamps switch, were not connected, yet.)

The lighting wire that goes from the ignition switch through the firewall was burned in two, close to the ignition switch. The wire from under the hood that returns through the firewall and goes to the rear lights was left mildly damaged, with some melting of the plastic covering (solid red in color) at the tail-light fixture. The melting was noticeable at the Right tail-light, but no melting at the Left tail-light.

It looks like the damage to the red lighting wires was the only observable damage. Signs of other damage haven’t been found, but the other parts of the harness have not been cut open.

Have you had a similar wiring accident? What steps did you take to evaluate and recover from the accident?

Thanks.
 
Re: electrical short wiring damage

similar but slightly different. when I was restoring Ms Triss, I found a few wires behind the dash that had fused together. I carefully separated and replaced with shrink wrap and same sized wire - no problems since. It might also be a good time to add a relay or two - though a relay wouldn't have helped you here as I don't think anyone has ever put relays on tail lights.
 
Re: electrical short wiring damage

And as a tip, as I will be doing this in another week or two, do not connect directly to car battery until all circuits are tested and you know there aren't any short circuits. Install a plastic fuseholder for a 5-7 amp fuse between battery terminal and the new harness. Test each connection individually and validate current is there. Do them in order and make sure everything works correctly before powering up the car battery. It will save you from buying another harness and may even save your car.
 
Re: electrical short wiring damage

Oh and make sure, are you converting from Positive to Negative Ground. Wiring for the most part remains the same but for someone who doesn't understand the difference that could be part of the problem. Rear wiring goes to the RR Tailight first and then jumps over to the LR Taillight. I'd think about replacing that entire piece that runs to the rear end. It's all bundled in the same wrap going to the rear.
 
Re: electrical short wiring damage

Just turning the switch on would not have caused a problem if a dead short didn't exist some where. You will have to assess how much damage there is and how to repair it by cutting open the loom. My BE had had a dead short wired in when I bought it. To find out exactly where the problem was I used a in line fuze holder wrapped around one of the battery terminal bolts at one end and held to the battery post at the other end by a small hose clamp. It took several fuzes but I eventually found a dead short at the dash light switch. Had to replace some wire and the ignition/lighting switch. Lighting contact's inside had acted as a fuze.

Kurt
 
Re: electrical short wiring damage

Thank you to JP Smit, Jim Gruber and Nomad for answering my call for help. I am un-educated about car wiring, but I want to work my way through this problem and learn something.

So far, it looks like the Red lighting wire that branches off to the back of the Bugeye was the wire that shorted (shorted at the Right Rear taillight), when the ignition switch was accidentally left on.
(All of the rear wires were connected to all of the rear light fixtures, with no bulbs in the fixtures.) ​
The Red lighting wires that branch off to the front of the car look undamaged. The front Red wires were all disconnected and apparently not shorting on the engine, frame or body.
 
Re: electrical short wiring damage

Hi Nomad/Kurt, Can you guide me to a source for how to find a dead short. I am a beginner at working on wiring. Thanks for any suggestions you can offer about understanding how you used the in line fuze holder, battery terminal bolt and battery post to test for dead shorts. Sid
 
Re: electrical short wiring damage

Sid; To start make a ( PIG TALE ) jumper with clamps on each end and a bulb socket between with 12 v bulb installed. ( all parts from auto parts store ) Make it long to move around car. First hook one end to POS. battery post with red battery lead off.. Two if any wire is grounded as you contact any plug, switch, fuse holder, wire end has a ground the light will light the same brightness as if you touched ground on battery. If not as bright you are looking for a pinched wire that has a poor contact to ground. You could use a volt ohm meter but leads may not be long enough. As you said most units are not hooked up. Lets take the tail lights wire at light base touching your red wire it should not light your test bulb. If it does that wire has a ground pinched wire or other problem that has been made by short. There are few circuits so should be easy to check each. NOTE horn and main head lights wires can be separate from back of car to front only. Ounce you have checked all with key off and find no problem do it again with key on. With the long leads tester you may do this alone and may wish to turn key at each test. In most cases a BLACK is a ground wire and RED, WHITE, GREEN, or PURPLE are hot feeds to circuits even if they have a color strip. Remember your jumper is a hot lead and the bulb will allow it to not be a direct short from your battery but may show a small spark as noted at NEG battery post.

Are LBC's are known for poor grounds and any wire can be problematic. I recommend installing and battery cut off some place on your car. Never work on any part of your car with battery connected. Any place where a ground is used make sure it is clean and any paint removed. Madflyer
 
Re: electrical short wiring damage

Hi Madflyer, Thanks a lot for the detailed instructions on testing for shorts. Sid
 
Re: electrical short wiring damage

Another way would be to use the fuze holder I suggested and just isolate suspected circuits till you narrowed it down. Use a low amperage fuze. The test light that I use is one of those little ice pick look alike's. I have a couple of Vohm meters but usually just grab the test light. You need a accurate wiring diagram that is color coded.

Kurt
 
Re: electrical short wiring damage

The inline fuze holder wired between the battery clamp and the battery post fuzes the whole system and with a.... say....5 amp fuze in the inline fuze holder you can blow as many fuzes as you wish and not damage the system. The fuze holder should be available at any auto supply store. If you are actually going to light the lights or put a load on a circuit you may need a 10 amp fuze.

Kurt
 
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