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So, I finally got my baby back after having the C6 rebuilt by a local mechanic about 2 weeks ago. It’s been bliss driving the 76 F100 again.
Till today, let me preface by explaining she sat 6-7 weeks without starting while I was finding and lining up the trans work. But when I did start her, she fired right up without missing a beat. Then today I was about to take a trip into town and nothing. No clicks, to noise, just silence. I thought there’s no way she’s dead, I just went on a 100 mile scenic cruise yesterday (where the 460 got an impressive 14.2 mpg while cruising 45-60mph for the majority of the ride with very little stops).
So I decide to jump her off, easy stuff first, and she fired right up. I was hoping the ECU didn’t crap out on me. I took her for a 45 minute cruise on the backroads close to home to let everything charge back up and as I’m pulling into my backyard…..puff of smoke and the smell of electric burn….then she died.
Pulled the dash, and found an ignition wire in 2 pieces fully exposed and burnt plastic casing. Now the harnesses I’ve found online look like they all have same diameter wiring compared to this one with multiple sizes coming from it.
Also the burnt line looks to be sharing a connector with another wire…is that normal or someone bubba’d it up? Then the other half going to a wiring harness looks like it feeds a bank of several other wires.
in hopes of trying to get a little life into her till I order another harness, I wrapped the ever loving **** out of the burnt wire (after reconnecting the 2 halves), but soon as I turned the key……smoke. So stopped all that and pulled the tape from the wire.
Is there anything else I need to look for as far as the cause, I’m thinking the wire probably wore in a spot and exposed to something else to cause it to fry?
Can you tell which color wire it used to be? If it’s on the same terminal as the red with green stripe wire, which is what it looks like, then it might be a green with red stripe wire.
But I thought those were on another terminal on these later years. Early models shared one, where later, like yours separated them.
or at least I thought.
What kind of work did you have done, other than the transmission?
Did you happen to change out an alternator for a modern internally regulated one?
Did you change anything in the starter system, or charging circuit?
Did your truck have an ammeter or a warning lamp for the charging system?
I’ll have to look at the wiring diagrams for your year when my vision isn’t so blurry.
But in the meantime, any more information you can give would be great.
Can you tell which color wire it used to be? If it’s on the same terminal as the red with green stripe wire, which is what it looks like, then it might be a green with red stripe wire.
But I thought those were on another terminal on these later years. Early models shared one, where later, like yours separated them.
or at least I thought.
What kind of work did you have done, other than the transmission?
Did you happen to change out an alternator for a modern internally regulated one?
Did you change anything in the starter system, or charging circuit?
Did your truck have an ammeter or a warning lamp for the charging system?
I’ll have to look at the wiring diagrams for your year when my vision isn’t so blurry.
But in the meantime, any more information you can give would be great.
When I get back from work, I’ll look for a bit of the wire, I know it’s red, but unsure if it had any other color.
As far as work, the original motor / trans was swapped with a 77s 460/trans. Other than that “I” haven’t had to do any alternator / starter / electrical. The ammeter holds steady just left of center, or at least it did right up till the moment it fried. I didn’t notice what it ready when the dash was smoking.
I guess my next question would be, how to tell what caused this. The ignition module male ends are fine and the group of wires this one feeds is fine, and the wire this one shared a terminal is fine. What could cause this one stretch of 4” wire go toasty.
Hey, sorry for the delay. I think I just cleared my PM box, and I'm way below the max now, but when I tried to PM you it still says my box is full. Well dagnabbit!
But try again from your end and see what happens. But I'll check out your post here now and see what I can see. Might have to take a brake for a sammich first, but I'll get 'round to it eventually!
Looks like it was orange, but got toasted to a fine brown color as it left the smoke siginals for you.
In fact, it looks from here as if the brown portion of the stripe was actually burned off completely! Is there any bare wire stranding there under your finger? Or is it just that the Red portion of the wire has swollen/expanded, making it look like the stripe has actually burned off?
We might have to continue the conversation here.
It makes sense anyway, but my PM box is still full even after emptying five or six messages.
I just tried to send you one, and it wouldn’t let me.
And it wasn’t even a big one!🙄
Ok, back to this finally!
Could that be a Red w/green stripe wire? Is it the one that looks like it goes into that factory splice in your earlier pics? The "splice" is that black blob of rubbery stuff that encompasses multiple wires. Very robust and solid splices from the factory!
But it looks like the wires coming out of the other side are Red w/green (ignition coil and other duties) and Blue?
Either way, revisit the other end of the splice and let us know just what wire colors come out the other side.
If it's Red w/green, that's probably splice #401 in the diagrams and connects a Blue wire to the ignition control module, the Green w/red wire to the voltage regulator, and a Red w/yellow wire that I have not followed yet.
It seems the melted side is between the ignition switch and that black splice? Something on any of those other circuits could have shorted out and caused the wire to overheat. You would think it might overheat first closer to the fault, but maybe it wasn't a true short, but just an overload. In that case it would effect the Red w/green wire at the ignition switch, because it's trying to carry the full load of all those circuits.
So suspects for now would be the ignition control module, the voltage regulator, or whatever that yellow stripe wire goes to. I'll kind of dig in and see where it goes in case that gives us more clues.
By the way... Does your truck have the older 5-fuse panel, or the later 10-fuse panel?
Should have the later one, but wanted to check since the diagrams are misleading by lumping all 75's and all '76's together. I've noted that the fuse panels are different on some, perhaps being either a running change, or just a very early or very late production change.
Also, does anyone have that nice diagram showing the "old vs new" ignition switches? Seems like it was a late-sixties change from the troublesome early switch that often melted down, but if it was a late-seventies thing, maybe that's at play here too.
I doubt it though, because I think by '76 they would all have been the updated version. And if memory serves, your connector is of the later type.
The other wire in this scenario (Red w/yellow or the Blue one) serves to power up two other accessory groups. One is the idle control solenoid at the carburetor, and the other is the fuel tank selector valve.
The problem here is that both of them are (theoretically) protected by their respective fuses (F5 and F3) and so should have blown a fuse before messing up a wire.
Unless the fuse(s) were replaced with higher rated fuses that have no business there? Have you checked all the fuses again?
Dual tanks? The valve is working ok? Carb solenoid working?
Well, neither of them is working at the moment I'd wager! Not with their main power source melted up at the switch!
Anyway, thought I'd add that little bit of info in case it ends up leading us in the right direction.
