I know there are lots of variables, but what do you think would have caused my headlight wiring harness to melt.

Car was fine, did a quick acceleration from ramp to freeway. Smelt buring smell. Volt gauge indicated a drop in voltage from charging to about 12 volts, than a burning electrics smell.

Left indicator came on, right indicator, both on steady and then the headlights popped up and on. No contol from signal indicator switch or headlight switch.

Even with car off, lights still on. Disconnected battery. No blow fuses, but fount melted harness. Some wires burned down to bare copper, a couple burned through. Lucky it didn't catch on fire!

Voltage surge, old wires, a short, all of the above?!?!

 

 

sounds like a bad connection, like a bare wire has been touching the frame or another wire and caused it to overload and melt, very lucky it didnt catch on fire,

if the whole light harness has been removed your best bet is to plug in a replacement one and try again, before plugging it in you could test the terminals where it plugs in when you hit the light switch, make sure theres not high voltage going through the connector otherwise it will happen again, and your problem will be further back through the wiring harness

 

Thanks for the replys. Now isn't it strange that no fuses blew or a fuseable link didn't let go? Nina, the breaker that you speak of, it is built into the switch?

Sounds like a short to me, but any possibility that the reving of the engine and a bad voltage regulatory could have contributed to this?

Perhaps old wiring being cooked over and over for 27 years is more probable?

 

ive recently had a problem where if i reved my engine the fuse for the dash gauges would blow, im not sure how i cured it but i had all my interior out doing stuff, so i put the carpet back in and pulled the wires through and its been ever since, so i think there was a dodgy wire somewhere.

still got some weird electrical problems going no now tho in another thread.

ive also had to put new connector blocks on both my headlights as the wires on there were so bare and brittle one of them finally gave up and snapped when i put my headlights on, so with age they do start going nasty, especially there as they are slightly exposed to water etc with the gaps in headlights

 

Bad design.

This business of running the full headlight current thru the cabin and light switch/breaker, thru little tiny wires, always struck me as odd when I first got my car. It's begging for stuff like melted harnesses and dim lights etc.

After my light switch started smoking and melting (great breaker action btw! NOT), I couldn't get a couple of relays up front fast enough, like every other car I've ever owned had factory.

 

So what you are saying is that even after it is repaired, good possibility of it happening again in the future. Better carry a fire extinguisher from now on

 

 

Is there any manually resetting of this breaker, or is it more like a thermal overload that automatically re-closes after it cools back off?

 

 

Back up and running again. Short was traced back to the left fog light. Lens casing grounded out positive lead, fused the wires running into the fog light casing and melted everything back to the c100. Did a full harness swap. Thanks for the replies.

 

Nice, glad you solved the problem! Thanks for posting back yourself - so many don't, really helps the next guy reading this thread

 

Hi. Sorry to jump into this thread at the end, I'm just new to this forum. But I have an 85 T/A and literally have the same problem. Fog light wiring on left side rubbed throught(looks like its been repaired before) and melted alot of the harness all of the way back to the firewall. My first question is whats a c100? and second where did you get your harness? I looked at Painless wiring and it looks like its going to be about $500+ or I thought about buying a old car for parts. We don't really have much in the junkyards around here.
Thanks for any help you can give. I'm almost at the end of my rope with this car, It was supposed to be ready to drive in May but everytime I take it out another problem develops.

 

C100 connector is the connection at the firewall by the brake booster where the wiring goes into the car.
To find a headlight harness look on the classifieds here and ask if the person says they are parting the whole car. Ask at Thirdgenranch or Hawks or look on ebay.
Get the correct headlight wire harness though. One with the same light setup as yours. I have a 91 with 85-90 T/A bumpers and ground effects so my original harness is not long enough in some places. I need a 85-90 T/A harness but made mine work.

 

Agreed. PM me if you want. I took some pictures along the process. The entire harness is connected way up in the driver side.

 

Thanks for the info, I really appreciate it. I'm working at a novice level when it comes to mechanical knowledge and I'm unfortunatly not a quick study. One other quick question is the little black relay on the drivers side fendor just up from the firewall the fog light relay? The wires split off from the headlight harness to it and are melted as well. Does it come with the harness?

 

Thanks to 85FBTranam for his detailed instructions. It doesn't seem as impossible anymore. Just waiting for the harness to arrive now.