Fired it up finally!! And… Electrical fire followed :)

[guidoverduci]

Well it was a brief moment of happiness, then it started smoking like crazy. I tried to investigate a bit and couldn’t figure it out. I decided to start it again and get some better eyes and angles, and I found the culprit. I’ve got a couple wires coming off the harness (which I assumed are reverse lights). I didn’t plug it into the harness on the new AX15 because I am awaiting a pigtail to attach to those to wires, and then plug into the transmission. I have NO IDEA why this wire would get so hot and start frying? It wasn’t lying on the exhaust or anything. Could I have done something when hooking up other electrical stuff that causes this? I’ve attached a pic, but there were other hot/melted spots further down the wire too.

 

[Jdgephar]

If you're melting a wire, it has way too much current going through it.

What harness is it? Stock Bronco? Something with fuel injection that was added?

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[guidoverduci]

It’s the Painless wire harness. I didn’t install it and didn’t mess too much with wiring. No EFI, there’s a 351w with HEI.

I think there’s a chance that the metal ends (that are supposed to be connected to the trans) were grounded against the frame. It’s definitely the reverse lights / neutral safety switch wiring. This was not a gradual thing. Engine turned on, and it started smoking pretty quick.

 

[Jdgephar]

The only thing I see that isn't fused in the painless schematic is the neutral safety switch wire. Just about anything else with a short like that would have blown a fuse. The NSS may have an exposed connector on it that could short to any metal around. I know you have a manual, but that doesnt mean the NSS wire doesnt have 12v on it. It just depends on how it was setup to work with the manual trans instead of auto.

Now it's time to find all of the melted wire, remove it, and replace any sections that are still required. Might have a section melted under the dash too if you have a clutch switch, plus the fact that it originates at the ignition switch.

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[stout22]

Sounds like a ground issue

 

[stout22]

I bought a Bronco one time that would smoke wires immediately after starting. Someone had put in a Centech harness but had not properly grounded the engine so it was picking up ground through a very small wire and immediately smoking.

 

[guidoverduci]

Sounds like a ground issue

I think you’re right. Found a ground strap hiding that wasn’t tied in. It was on the frame and looks like it was once attached to the starter bolt that goes in the bell housing.

 

[DirtDonk]

The red with blue NSS wires are only hot when the starter is cranking. But they are probably jumpered together or the starter would not have cranked the engine.

The black with red back up lamp wires are hot anytime the key is ON or in ACC. Well, one of them is hot anyway.
The other goes to the back up lamps.
If the hot side wire was touching a grounded bit of metal that would do it.

And since Ford also used black with red coloring for some ground wires, I would definitely follow that wire all the way to its end to make sure it wasn’t used as a ground.
I know you said this smoked after startup, but did you run the key on at any point to test the electrical system?
And it wasn’t smoking then? If not that would be a strange arrangement.
It should’ve melted as soon as the key was turned on.

But it’s all speculation. Follow the wire and see where it goes. And it said, see how much of it is melted.

 

[guidoverduci]

The red with blue NSS wires are only hot when the starter is cranking. But they are probably jumpered together or the starter would not have cranked the engine.

The black with red back up lamp wires are hot anytime the key is ON or in ACC. Well, one of them is hot anyway.
The other goes to the back up lamps.
If the hot side wire was touching a grounded bit of metal that would do it.

And since Ford also used black with red coloring for some ground wires, I would definitely follow that wire all the way to its end to make sure it wasn’t used as a ground.
I know you said this smoked after startup, but did you run the key on at any point to test the electrical system?
And it wasn’t smoking then? If not that would be a strange arrangement.
It should’ve melted as soon as the key was turned on.

But it’s all speculation. Follow the wire and see where it goes. And it said, see how much of it is melted.

Thanks Paul. Yes, before starting, I ran they key in ACC and on. Tested a few things, all seemed normal. I didn’t notice any smoking. I was in ACC for awhile too. ON for just 15 ish seconds while the electric fuel pump ran.

I’m tracing the wires now. I know I forgot a ground strap as stated above. And there’s a good chance the metal ends of NSS / reverse light wires that attached to the old manual trans were touching the frame when I ran them engine.

 

[DirtDonk]

Then the damage should be pretty minimal I would think. Hopefully limited to just that/those wires.
I wonder if Painless does not activate that circuit in ACC? Might be why it acted the way it did. The factory harness has it hot in both positions, but nothing says Painless could not change that to ON only.

Paul

 

[guidoverduci]

Then the damage should be pretty minimal I would think. Hopefully limited to just that/those wires.
I wonder if Painless does not activate that circuit in ACC? Might be why it acted the way it did. The factory harness has it hot in both positions, but nothing says Painless could not change that to ON only.

Paul

Yep, looks like it was limited to that wire. Fried it all the way back to the ignition switch.

 

[DirtDonk]

Well there’s something interesting. That wire should never go directly to the ignition switch.
What color was the wire at the ignition switch?

 

[guidoverduci]

Well there’s something interesting. That wire should never go directly to the ignition switch.
What color was the wire at the ignition switch?

black/red and was on the post in the center.

 

[guidoverduci]

Here’s a pic of my ignition sw for reference. The black red was on that center post under the rubber boot. Other wires on there, yellow, red/blue, green/red, green/black, and green spliced into a red.

 

[DirtDonk]

Well, better check around the fuse panel also.
Is that the only wire on the center stud? I know Painless kind of messed me up when they designed the harness originally because most Early Broncos use only a black with green striped wire and not a black with red stripe.
But I remember the harness had something switched around and maybe this is it.

But the center stud is literally the main switching for ACC power it’s hot in both ACC and ON.
It should not run directly from the ignition switch to the reverse lights.
I’m glad everything else is be working though. That’s a good sign.

 

[guidoverduci]

Well, better check around the fuse panel also.
Is that the only wire on the center stud? I know Painless kind of messed me up when they designed the harness originally because most Early Broncos use only a black with green striped wire and not a black with red stripe.
But I remember the harness had something switched around and maybe this is it.

But the center stud is literally the main switching for ACC power it’s hot in both ACC and ON.
It should not run directly from the ignition switch to the reverse lights.
I’m glad everything else is be working though. That’s a good sign.

Yeah, it’s weird for sure. This electrical stuff confuses me, but I can figure out enough to get by.

There was a black green wire on the center stud under this one. I traced the fried one all the way back, it’s not spliced or tied into a fuse panel even though it looks like it should be according to the painless diagram. It just goes straight to a pigtail plug and into the transmission.

Should I route a new reverse wire differently? I need to wire in this pigtail for the ax15.

 

[DirtDonk]

Interesting. That black with a green stripe wire looks like an original factory wire.
Do you have a painless instructions handy? If so double check how they wire the switch.

Since there should be a fuse for the back up lamps I’m not sure why they would have a direct wire.
I don’t see any legitimate reason for that wire unless something is wrong with the one from Painless fuse panel.

 

[DirtDonk]

Do any of the wires also have a writing on them? If it’s a Painless wire it has writing. If it’s a factory wire or substitute it would not have printing on it anywhere.

 

[guidoverduci]

Do any of the wires also have a writing on them? If it’s a Painless wire it has writing. If it’s a factory wire or substitute it would not have printing on it anywhere.

That’s interesting. I haven’t seen writing on any wires, but (for the most part) the colors match the painless instructions and it’s the same fuse block and setup shown in the instructions. The ignition sw instructions, however, are a little different…

 

[DirtDonk]

Yes, Painless substituted their black with green wire for the original red with green and green with red wires in their kit.
Then they substituted an orange wire for the original black with green.
Looks to me like your ignition switch has remained with a replacement pigtail and connector and then it was spliced into the Painless harness wires.

That connector on the back of the switch looks to be one piece with the wires molded in. That tells me it’s a replacement because the original was equipped with a flat plastic panel on the back to cover the exposed connectors.