Saw small amount of smoke from driver speaker opening and defroster vent when starting up 76 after body off and complete restoration. Took out dash and console and found melted wrap on dash wiring bundle. Tore off wrap and found the melted wire (see photo).
It was the wire from the Ignition Switch to the Alternator. It provides the signal to the Alternator. No fuses were blown. Turned out to be Alternator signal circuit in regulator had failed to ground. The only damaged wire was the section where extra wire had been wound up inside the bundle (original GM wiring harness). If this had happened while driving it with the tops off might not have noticed the smoke until it caught fire or battery died. Now thinking about putting a fuse or something in the circuit.

Anyone have any other thoughts?
Bob

 

"Turned out to be Alternator signal circuit in regulator had failed to ground."
From this statement it sounds as if you have fixed this , is this true ?

If its not fixed are you sure you didn't reverse the 2 wires at the alt plug ? That brown wire circuit doesn't really carry a load but if reversed at the alt its possible it could be loaded by the heater circuit. Did you have your heater blower on when the wire melted ?

 

Roger-
Many thanks for your comments. I respect your knowledge on wiring as evidenced by your previous postings.
It is fixed and runs fine as of last night with all the wires nice and cool. Pulling apart and re-assembling the dash is not one of my favorite projects!
The wires to alternator were not switched while I have had it, but before I got it I can't say.
Heater fan wasn't plugged in when it was started up. I am interested in how you think this may have caused the failure. I don't see the heater in this circuit.
This car had a lot of Bubba's in it when I got it and a lot of extra wires for door solenoids and stereo junk which have all been removed and taken back to stock.
When I got it 3 years ago, it only ran enough to get it on the trailer and into the garage before it was totally disassembled. It took a new battery when I picked it up to get it started as it had been sitting for awhile.
Considering all the other things I found I suspect that it was blown when I got it. Because it had run I didn't check the alternator before starting it back up. This is now on my check list for the future!
When I looked at the wiring diagram, there is nothing else in this circuit. (Brown and While wire 24 from ignition switch that is plugged into Brown wire 900 to alternator)
There was about an extra 8-10" of the failed wire wound up in the harness and this is where it heated up. The harness did not look like it had ever been touched in this area.
This one concerned me enough to post it because of the fire potential. When I look at the circuit if it does go to ground there is enough fused amperage available to cook this wire without blowing the fuse. Brown and White wire 24 is really small and it wouldn't take much amperage to heat it up.
Thanks again for your help,
Bob

 

The orange from the ign switch that the brown connects to supplies the the heater fuse. Definitely a long shot and the 2 wires would have to have been switched,doesn't sound like this was the case but I have seen it happen when the alt plug pigtail is replaced with an aftermarket.

I will add ,one part of the brown wire circuit is a resistor wire,I think its the 24 gauge part.

 

Roger:

74 big block coupe;

just caught this thread and have a question... my alt has the 2 tabs in the connector numbered as '1' and '2'. I have ofte worried about a switched wire by previous owner. Which wire goes to the '1' tab?