My 1988 F250 4x4 7.5L 460 XLT with c6 transmission stalled out today. Smoke was coming out of the engine compartment and one of the wires from my fuse block was smoking. I have no idea what it goes to or comes from other than it goes into my wiring harness and comes from my fuse block plug inside my engine compartment against the firewall on the drivers side. It's only that one wire that is damaged. I thought I could do a quick splice and when I turned my key to the on position (without starting) it got red hot instantly and melted. My truck will not start without that one wire being connected, but I'm not sure what it is for or even if that is the problem (other than the obvious that something is seriously wrong with the electrical). To me it seem like there is a short somewhere in the wiring harness, but I have been though it the best I can in the dark. I didn't see any other damaged wires at all and I have checked all the fuses I could find. None are blown. All my instruments work and lights, radio, horn etc... Would that one wire cause my truck not to start??? And why is it getting red hot instantly when I turn my key to the on position??? Any advice at all would be appreciated tremendously!!!

 

definitely a short circuit. you said it goes along the firewall? run a seperate jumper wire in place of it and see if it works. if it does, it's shorting along the firewall somewhere.

 

Is it a "factory" wire or one someone added for whatever reason, I ask because it should blow a fuse or fuseable link before a wire goes that bad.

All fuses installed are rated correctly far as you know? I mean didn't nobody do something like fill the box with 25-30amp fuses did they?

If you're sure its a factory circuit post the color of the wire in question.

 

No, it goes into the main engine compartment wiring harness connector that plugs into my fuse box on the inside of my cab under the steering wheel. The other end of the wire goes through my engine compartment I'm guessing over to my starter relay mounted on the passenger side of my engine compartment on the fender???

 

if it's a factory wire, someone COULD have removed the fusible link (why? i'll never know). or it could be shorting before the fusible link? also, post up pics of exactly where this wire is going. and possibly pictures of it smoking, because smoking's still cool, right?

 

I couldn't really see in the dark, but I believe it's red/light green. It was definitely a larger diameter than the others unless the color was making it look larger than the rest. I'll be able to say more tomorrow when I tow my truck home. I guess I was really hoping I would be able to do a quick fix to drive it home instead of towing it and address the problem in further detail once it was here.

 

lol, I'll post pictures of it tomorrow when I get the truck home. It's factory for sure.

 

If it gets hot only when the key is turned on then doubt its one that runs between the fender mounted relay and fuse box.

Is the wire yellow?

Gray with a yellow stripe

Red with a light green stripe

Black with a light green stripe

 

Red with a light green stripe is ignition switch/coil & coil/battery.

 

Ok. The wire coming from the fuse panel connection is a thicker red with green stripewire and it's connected or (burned through the splice that was made) to a yellow with a blue stripe wire. Any ideas???

 

Here's the schematic.

From the ignition switch is a Red/Light Green wire that is hot when the ignition
switch is in Run or Start.

Provides 12 volts to the dash charge indicator lamp which then goes to the
alternator regulator.

The Red/Light Green wire is Spliced to a 20 gage fusible link located LH side
of engine compartment. The wire turns into a White/Light Blue wire.

This wire provides 12 volts to the following.

TFI module.
12 volts for the coil.
12 volts to the radio noise capacitor. (I think should be near the distributor).
12 volts to the EEC relay coil.

The Red/Light Green wire also provides 12 volts for fuse #18 and fuse #15.

Fuse #18 is 12 volts for the Brake warning indicator.
Check Engine indicator.
12 volts for the seat belt headlight on chime module and
dash gauges.

Fuse #15 is used for the Diesel fuel tank selector valve.

 

Got it!!! Thanks for the schematic. The problem was that the wiring harness connection going to my ignition coil. The coating of the wire pulled out of the connection and was grounding itself to the valve cover. I lifted the connection off the valve cover and spliced the red/light green wire to the yellow one and my truck started. Thank you all for you advice and especially for the schematic. You all saved me a lot of time and one huge headache of tracing wires. Thank you all!!!