Electrical Fire - Under Dash

[BruiserOutdoors]

Had an electrical fire under the dash. Happened while at the exhaust shop, so I wasn't there to witness. Apparently it happened within 10-15 seconds of start up. It appears to have only affected the stock harness and not the Quick 4 Harness that is right next to it.

At my own fault, I had just stuffed some of the loom of the quick 4 under there to push it out of the way. It seemed like the worst damage was a possible ground wire to the stereo. It was barely touching the ground for the ignition switch when I first looked at it. The end of this wire is now broken/fallen off so it doesn't show in the video. I plan to post the video on Youtube tonight for you guys to look at. Yes its a rats nest. One of those "if it aint broke, dont fix it" scenarios. Well now its broke. My dad, the owner of the bronco, is tempted to just drop the whole project and have a new harness installed (which would probably snowball into a color change/repaint). I would rather get it back and operation for a few more years to come if possible.

Some more of the backstory. Just installed a 347 stroker, pf4 efi, 4r70w, quick 4 controller, etc... I had messed with the ignition switch wiring when dealing with the NSS. I took off the ground and eventually reassembled and reused the stock harness plug to wire the NSS.


Thoughts? Advice? Could it have been as simple as the stereo ground wire improperly attached the ground of the ignition? Or a wire shorting out?


We are very fortunate that the fire was extinguished when it was. Much more damage or loss of the vehicle could have definitely occurred.

 

[DirtDonk]

Wow, could’ve been a lot worse! Glad it’s still in one piece and sounds like everything is toast.

But first off, there is no ground on the ignition switch. If you were touching that center stud with the black wire on the ignition switch, that is power for the accessories in the fuse panel and a few other places.
So never touch that with a ground!

 

[DirtDonk]

Stereos are often causes of problems as well. Sometimes they draw big amps have big wires that put out a lot of smoke.
Also, with all the modifications, have you put a more powerful alternator in the system?
If so, is it run through the original wiring? If so, that could be a problem as well.
But if that ground wire was touching the ignition switch, that’s likely your problem.

 

[joebronco73]

One of those "if it aint broke, dont fix it" scenarios.

Just to clarify/add to this saying: you can't fix it if you don't KNOW its broken.

With that in mind, I'm of the thought that you should either: diligently spend some time checking the wiring OR spend the money on a new harness to avoid any bad patches and failing wiring. Honestly, it would be a shame to lose a new engine and the whole bronco to an electrical fire that could have been prevented. The questions are: what is the intended use for your bronco (daily, weekend/leisure, or off road only) and what is your budget? Those two questions should get you pointed in the right direction.

 

[SteveL]

If you played with the ignition switch make sure all the prongs are actually inserted where they plug into the harness. When I rewired the 66 with a centech it was fine for a few months then smoke under the dash. The switch and a couple wires melted. I called centech and they said it's common for a blade to miss its female counterpart but rest up against it. It works for a while but generates heat until it fails

 

[BruiserOutdoors]

Stereos are often causes of problems as well. Sometimes they draw big amps have big wires that put out a lot of smoke.
Also, with all the modifications, have you put a more powerful alternator in the system?
If so, is it run through the original wiring? If so, that could be a problem as well.
But if that ground wire was touching the ignition switch, that’s likely your problem.

Yes, Explorer serp. with a bosch 4g Alternator. Runs at about 14.2 volts at idle.

 

[DirtDonk]

And you have a big, battery cable size wire, running directly from the BAT output stud of the alternator, to the battery side of the starter relay/solenoid. Correct?

 

[BruiserOutdoors]

And you have a big, battery cable size wire, running directly from the BAT output stud of the alternator, to the battery side of the starter relay/solenoid. Correct?

Yes. The bronco has ran for 20-30 minutes now, so it seems like that would have affected things sooner.

 

[BruiserOutdoors]

Wow, could’ve been a lot worse! Glad it’s still in one piece and sounds like everything is toast.

But first off, there is no ground on the ignition switch. If you were touching that center stud with the black wire on the ignition switch, that is power for the accessories in the fuse panel and a few other places.
So never touch that with a ground!

Yes I meant the center stud. Thought it was a ground for some reason. You would think if that was such an issue it wouldn't be designed to be exposed like that?

 

[DirtDonk]

There’s a great example of a best practice about that, in another thread about another a meltdown from a couple of years ago.
In that case, it was something else, but the owner had installed a small piece of rubber hose over the stud.

But from a safety standpoint, if it’s not messed with then there’s nothing to happen. There’s nothing back there exposed that could touch it. It’s completely isolated from other wiring and other components.
Only if we make some kind of a mistake, does it come up as an issue.
But you’re right, maybe after all this is said and done, you’ll take a small piece of quarter inch rubber hose about an inch long and slip it over the stud.

 

[DirtDonk]

Yes. The bronco has ran for 20-30 minutes now, so it seems like that would have affected things sooner.

Yes and no.
With the big cable connected, there’s no danger of overpowering the original system. As long as the original black wire is disconnected that is.
But you can run it for a long time even on that original 10 gauge wire if the alternator isn’t required to put out much current. Such as to recharge a dead battery.
However, if the battery is very low sometime, and the alternator is really putting out high current levels to recharge it, it could easily melt the original wire under the dash.
Most re-wires, where you add a large cable from the alternator, include disconnecting the big black wire from the back of the alternator.
Even though right now we suspect something touching that ignition switch stud, hopefully you still left the old Black wire off of the alternator.

 

[BruiserOutdoors]

Here is a quick video of the wiring. Please take a look and let me know if you notice anything....

The smoked wire that runs all the way to the stereo was IN FACT touching the stud terminal on the ignition when I first looked at it. Again, the ring terminal crumbled off before the video. This wire may or may not be a ground for the stereo. I have a feeling it wasn't, and used to be attached to the stud terminal of the ignition?

Looks like the firewall/cowl insulation burnt up a bit. Got real lucky.

 

[BruiserOutdoors]

Yes and no.
With the big cable connected, there’s no danger of overpowering the original system. As long as the original black wire is disconnected that is.
But you can run it for a long time even on that original 10 gauge wire if the alternator isn’t required to put out much current. Such as to recharge a dead battery.
However, if the battery is very low sometime, and the alternator is really putting out high current levels to recharge it, it could easily melt the original wire under the dash.
Most re-wires, where you add a large cable from the alternator, include disconnecting the big black wire from the back of the alternator.
Even though right now we suspect something touching that ignition switch stud, hopefully you still left the old Black wire off of the alternator.

I followed your advice from post #15 here: https://classicbroncos.com/forums/threads/4g-wiring-for-dummies-like-me.281353/#post-3554668 , I believe. I capped off a bigger black wire and the only other big black wire was the "defacto" power source wire with fusible link that is still intact and in-use.

 

[gnpenning]

A side note, what type of fire extinguisher was used and has the residue been cleaned up??

 

[ssray]

Wondering as well if under dash fires could be handled by those Element extinguishers. No residue and out of the wind which I felt might hurt their effectiveness. CO2 would be no mess if they lasted long enough to do the job. They seem to be pricy but not what Halon costs.

 

[BruiserOutdoors]

A side note, what type of fire extinguisher was used and has the residue been cleaned up??

Human Breath. No residue. lol

 

[joebronco73]

Wondering as well if under dash fires could be handled by those Element extinguishers. No residue and out of the wind which I felt might hurt their effectiveness. CO2 would be no mess if they lasted long enough to do the job. They seem to be pricy but not what Halon costs.

From what I've seen of the Element extinguishers, they wouldn't handle much. If you have nothing else, sure, but better to have a dedicated CO2 extinguisher. There was a thread on this not too long ago:

Which fire extinguisher and how are you mounting it

Which fire extinguisher are folks recommending these days and how are you storing it? I don't do any off road with mine - I haul two kids (4 &10) and a dog - but my truck is such that if it caught fire anytime I would be surprised but not shocked. Seems like a good thing to have just in case.

classicbroncos.com

Link to a video demonstration of a variety of extinguishers:

 

[DirtDonk]

Thanks for the underdash video. But I can’t really tell anything from watching as you pan by the different sections.
It’s definitely a rats nest under there, like most Broncos are nowadays. All I saw were a lot of splices, a lot of loops with extra wire, and what looked like non-factory wires that were burned.
Looks like the damage was in a harness with all gray wires and that’s not standard Bronco stuff.

I don’t remember from your first post whether you said this or not, but does everything work still? Does anything work?

 

[BruiserOutdoors]

Thanks for the underdash video. But I can’t really tell anything from watching as you pan by the different sections.
It’s definitely a rats nest under there, like most Broncos are nowadays. All I saw were a lot of splices, a lot of loops with extra wire, and what looked like non-factory wires that were burned.
Looks like the damage was in a harness with all gray wires and that’s not standard Bronco stuff.

I don’t remember from your first post whether you said this or not, but does everything work still? Does anything work?

Havent been brave enough to hit the key again. I was going to cut some zipties, unplug the radio harness and assess further first.

Here is a photo of the loose wire with fork terminal that seems to have burnt up for its entirety and leads to the back of the radio. This photo was from a few months ago.

https://www.dropbox.com/scl/fi/4c8q...ey=kjgexwd589zuiox68m3287tgx&st=ziqix945&dl=0

 

[rocknhorse76]

Havent been brave enough to hit the key again. I was going to cut some zipties, unplug the radio harness and assess further first.

Here is a photo of the loose wire with fork terminal that seems to have burnt up for its entirety and leads to the back of the radio. This photo was from a few months ago.

https://www.dropbox.com/scl/fi/4c8q...ey=kjgexwd589zuiox68m3287tgx&st=ziqix945&dl=0

From what I’m seeing in your video, the wiring that burned up seems to all be for the aftermarket stereo, and none of the factory wiring was damaged. Unhook all of the stereo wiring and get it out of the way so you can see the dash wiring better. Also, that wire with the fork terminal on it was most likely a ground wire. If it touched the post on the back of the switch, it would definitely look like it does now. I used to install stereo systems as a side gig back in the day, and a lot of aftermarket head units would have a terminal like that installed on the ground wire.