My 1972 Stingray recently underwent a meltdown of the Brown/white resistance wire that runs from the ignition switch on the steering column to the Alternator/coil. 350 Small Block, auto Trans, A/C. Original wiring harness.
The meltdown appears to be confined from the ignition switch to the inboard firewall fuse block. I am on the process of replacing dashboard and power windows wiring harnesses. I have not yet determined the source cause of this meltdown. Any ideas???

 

Rookie reply...leaving the Ignition swith in the ON position too long will melt the wire or coil if the fuse does not blow.

 

That is an interesting thought that had not occurred to me.
Do you mean the “Start” position when you refer to the “On” position?
I was driving the car at the time. Had been driving nonstop for about 15 minutes.
Are you suggesting an ignition switch (on the steering column) failure? Or could the problem be in the ignition key mechanism higher up on the column?

 

No I think he was referring to leaving the key on the ON position but not running. If you leave it on the ON position but not running and the points are closed - that can act like a short. But since you were driving in this case it doesn't seem to apply. I assume you were left stranded on the side of the road since this happened while driving - that sucks.

Check that the resistance wire wasn't 'grounding' somewhere. Unfortunately last time I looked for a resistance wire I couldn't find one so I don't have anywhere to point you to for a replacement. Hopefully someone else will.

 

The wire from the ignition switch to the fuse block is NOT resistance wire. The resistance wire begins at the engine side of the bulkhead connector and runs to the ignition coil. For the regular wire under the dash to have melted/fried, that circuit must have had [nearly] a dead short on it. You must have some other issue with the wiring to cause that.

 

Actually it did not leave me stranded.
I had been driving normally for about 15 minutes. Suddenly without warning Smoke was pouring out around the dashboard, so I stopped and grabbed my fire extinguisher, expecting a fire. Smoke stopped and I could not find any evidence. Started back up, drove about a mile, and same thing happened again. I could find nothing. The most recent thing I had done was to replace the brake pads, so I thought maybe the brakes have overheated. Since I was near an exit ramp, I started back up and drove to the nearest parking lot. Got out, checked out everything, could find nothing. The ignition seemed to work well, start easily, ran well, and turned off without any difficulty.
Finally I start back up and drove about 5 miles home without any issues. Parked the car in the driveway and let it cool off. Looked again and found nothing. Later I backed the car into the basement, jacked it up, removed the tires and checked the brakes. Brakes were fine. A few days later I get up under the dash and after much inspection found melted wiring insulation in the dashboard wiring harness. In horror, I disconnected the battery immediately, which I should have done when I first parked it. After considerable effort I found that the resistance wire had melted down and burned into! It had also melted the insulation on other wires around it. I never could verify that the copper in other wires was exposed or shorted out, but I expect that was the case. The resistance wire is a brown wire with a white stripe and runs from the ignition switch to the inboard fuse block, and I assume from there to the coil. It is a small solid wire, not braided. I’m not sure that it is copper. It had actually burned into! I have not found any damaged wiring under the hood outboard of the firewall fuse block. I also have not found a blown fuse. That really is disconcerting. A fuse should have blown before something like this happened!
I am in the process of completely replacing the dashboard and power window wiring harness with new ones from Lectric Limited. I am concerned about the engine compartment wiring. I am finding some unexpected low resistance to ground on several of the pins in the engine compartment fuse block. I suspect that I have a short to ground on some component under the hood. I am reluctant to reconnect the battery until I have found the cause of the wiring harness meltdown.
Thanks for any insight you may have.

 

And the engine ran fine while this smoking wire was taking place? I would suspect something in the ignition system was shorting out. But that would prevent the engine from running, I would think. Bad ignition coil? Defect in the add-on ignition box (if you have one)? Ground short inside the distributor (I HAVE had the intermittent short in the distributor happen to me)? Something of that nature might result in over-current to the ignition switch wiring.

 

Yeah. Engine appeared to run as normal. Started flawlessly and shut off promptly. It was on a beautiful sunny day, so I was not using wipers, lights, heat or A/C. Only thing that might have been live was the radio, the signal lights, brake lights, etc. I have not found anything that is not working.
I am suspicious of the horn relay, so I have replaced it and the ignition switch on the steering column. I have removed all the dashboard wiring harness (what a job!), and find nothing suspicious except for the fried brown wire with the white stripe going from the ignition switch to the firewall fuse block.
How would you test for a short in the distributor?

 

Brown wire with a white stripe from the ign switch goes to the alternator according to the wiring diagram I have.

 

If I saw smoke coming from under the dashboard I would isolate the battery right away from the car's electrical system. I am a paranoid person and I still have my Chrome HALON Fire extinguisher in the car just in case. It sounds like some of the wiring harness under your dash might need to be replaced. I would check and double check every wire to verify that your short is long gone.

Electrical fires are some of the "worst" on older cars. I was surprised at how the wiring was done under the dash on my 1968 C3. I spent lots of time "cleaning up the wiring to help prevent shorts in my dashboard. I did not modify it, I just wire tied the wires together and made less stuff moving around under the dashboard.

If you feel the need to have a battery disconnect then I would suggest the knife style as the connection is made and done, the screw down type battery switch has the issue of and breaking the connection as it is screwed down. By making and breaking the connection multiple times very quickly you might damage some electronics that require their components to get charged up. It is better to have a quick On/Off of the power. I use a Marine Circuit Breaker as my disconnect switch as well as protecting my battery from a bad short. They are water-resistant and some waterproof even and they work well in a old convertible.

I would also do a close check of your alternator to be sure that it is not damaged. If the connectors are potentially corroded or dirty DEOXIT is an awesome electrical contact cleaner. This material will remove all the corrosion with a simple wipe. This material made my tail lights brighter after a simple cleaning of the socket. I use it to clean and protect my wiring harness in my Corvette. DEOXIT is available at Amazon or even Graingers.

 

Thank you for you suggestions.
I am currently replacing all my dashboard and power window wiring harness with a new set from Lectric Limited. So far I am extremely impressed with the new harness. It is exactly like the original one I just removed.
I am definitely going to install a battery quick disconnect. I am most fortunate that I did not have a catastrophic fire.

 

You can check for shorts in the distributor *and elsewhere* with a multi-meter continuity tester or one of those test lights with a battery and bulb in it. I wouldn't think the engine would run if the distributor shorted especially not to the degree that a short could melt/burn a wire and I guess you could argue that the distributor actually shorts by design every time the points briefly close and induce current thru the coil anyway... As 7T1vette posted previously I don't think that's the distributor resistor wire that melted - that wire is on the other side of the firewall. (I think a pink wire runs from the ign switch to the firewall bulkhead which connects to a fabric sheathed resistor wire to the distributor - but confirm that)

On m my '71 diagram there is a brown/white wire from the alternator to the ign switch. Following the flow of electricity... that would suggest to me the short is in the wire (close to the switch at/after point it melted, failed insulation for example), the ign switch (you've replaced but test the old one) or ign switch connector (old harness) or possibly further 'down stream' from the switch...

Wow - big project to replace that harness. Thanks for the feedback on their harness. Nevertheless I suggest you track down as best you can a definitive source for that short if at all possible.

Not directly related to your short problem but 2 comments...

I'll second the mention of a (Frankenstein style) blade type battery disconnect (negative side). I had the spin **** disconnect but thanks to suggestions here switched (pun purely intentional). The Frankenstein blade switch is quick, easy and visually you can tell it's state. It's discrete too - unlike the **** that 'flickers' the connection for a few turns...

I've also seen posts here for converting from an ammeter to voltmeter on earlier years. If/when I were into my dash again and/or replacing wiring - I'd probably consider removing the heavy ammeter wiring and switching to a simpler low current voltmeter in the dash. That's a big heavy gauge wire carrying some current for the old school ammeter. A voltmeter seems much safer and simpler to me.

 

There is no "heavy ammeter wiring". It's just two little 18 awg wires that carry some small (millivolt) voltage to the galvanometer that has an AMPS scale on it....