This wire is getting HOT!!!

[Blue71]

71 Bronco,302, MSD coil, stock style voltage reg, everything else is stock. Died several times as if u cut the key off. Limped it home by restarting it multiple times.. got it to my garage and it seemed fine for a sec. tried to drive it again and it would just quit.... no stumbling...I mean like Power was cut. Now it won’t fire up at all...I can just crank it . Noticed a little burn smell and saw a slight stream of smoke from behind dash/cluster, ignition switch area and found a very very hot wire. It looks like a larger wire with factory heat shrink. It comes out of the factory bundle and then makes a u-turn and goes back into the bundle. It gets hot while trying to crank the bronco over as well as if the key is in the on position. I followed the factory harness bundle behind the dash as it goes past the radio hole, ash tray towards the glovebox and the factory tape has a few melted places . Any idea what would cause this?

 

[Jfryjfry]

High resistance for the current would cause heat. But I’m not sure what that wire is. Is it a wire or a small wrapped bundle?

 

[Steve83]

You need to either pull the harness out, disassemble & repair it; or find each end of that wire, cut both, and overlay a new wire. If you turn the key on even one more time, the old one MIGHT melt through to any number of OTHER wires, shorting out the whole harness & setting fire to the truck. It's called a "cascade failure" because the first wire it shorts into gets hot, potentially shorting into several others; each of which can repeat that process in seconds.

You also need to find out WHY it's happening, but you can't really do that until you find out WHAT circuit that is. Can you see a stripe on that wire? Is it a an extra loop of the 37B Bk/Y or 38 Bk wire that goes through the ammeter?

(phone app link)

 

[Broncobowsher]

Do not attempt to drive. In fact, go unhook the battery cable now. You have a burned up harness. It has damaged other wires in the harness, guaranteed. I can't say what that wire is but you have a problem that needs to be addressed.

That picture of the burned wire inside the harness gives me chills. You have no idea how close you were to posting a thread "my truck burned to the ground". Yea, it is that bad. This isn't a fix a wire and keep driving repair. This is a "fix the harness", find where that wire goes in the process, and fix that problem as well.

 

[BajaBronco]

Blue,
I had a similar problem in a 69, mostly stock. Alt had fried and it burned up the same wire I think. It’s an old fuseable link wire designed to burn if it’s the same wire and it sure looks like it. I had to dig apart harness, cut wire (visibly melted) and splice in new fuseable link wire. Was after I found burned alternator of course. Anyway, some nearby wires needed repair too. But it’s all back together and been fine for over a year. Died just like you said but only 2x and 2nd time was all the smoke. Maybe you have a bad alt or connection somewhere on the charging circuit and it’s not fully failed yet. Batt post on my alt was cooked and wiggling around. Unplug and go check your alt.

 

[blubuckaroo]

Is this a case of too much alternator for the stock power cable?

 

[Pa PITT]

I'll say a bacd Ground somewhere .. But finding it now that's another story.

 

[DirtDonk]

What year is this Bronco? Is this the '76 or '77 by any chance?
The first picture with the circle does in fact look like your ignition circuit's resistor wire. It's routed separately from the others and in it's own jacket because it does get hot and can damage adjacent wires.
You should be able to peel some of that back and verify it's color and type.

Are you sure that's the same wire that melted the harness though? Does not seem like it should be, since the ignition wire does not travel over to that side on any year Bronco that I know of, It should got to the firewall in front of the driver and, depending on the year, exit the firewall in various ways.

Guessing this is a '71 or newer because of the size of the bundle running across to the passenger side?
As all the others have said, don't drive it, don't pass GO and open up that harness to see what it actually is.
I could be wrong, but to my knowledge the ignition circuit should not be over in that branch of the harness.

On a '71 and later, if you eliminate the fuse panel circuits, the only things that should be there are:
1. Lights
2. Voltage regulator.
3. Horn relay power and ground (if a '74 or later)
4. Main battery power and main charge cable (different ends, same loop of wire)
5. Red w/blue starter relay "S" wire.
6. Brown starter relay "I" wire.

Probably something else but I can't think of any others at the moment.
Trying to think of which of those could possibly kill a running engine it seems like the Brown wire would. But why it would short out, or what it would short out on, would be a mystery. The starter relay failing internally could do it. As could a fault in the wire itself.

More work ahead of you for sure, but at least you found it (smelled it!) early. Hopefully it's early enough that it did not actually compromise other wires too.

Good luck.

Paul

 

[jckkys]

I happen to have a '71 harness out of any truck. It has the same loop,so I started cutting tape. It turns out to be the resistance wire between the ignition switch and the coil. I cut a lot of tape and stabbed my thumb in the process. As un-burned it has resistance printed the whole length.

 

[rguest3]

Looks like it's time to replace the Whole Harness to a new one. Who knows what other hidden wires could be damaged as well? Not worth the risk of a completely lost truck due to a fire. Those are 40+ year old damaged wires you are relying on.

 

[jckkys]

Once you cut the tape wrap you'll know if the damage includes other wires. A new harness is a big job.

 

[jckkys]

I just looked again at the '71 harness and found that a 3 prong plug about 3 ft. from the coil is one end of the resistance wire the other end is in the ignition switch connector. The length of this resistance wire determines the impedance or resistance. The heat to melt the insulation implies a dead short.