Well, ran my 74 F100 for the first time this year a few weeks ago, and whilst out I got a puff of smoke come through the vents along with an electrical smell... Nothing stopped working, and I couldn't see any damage anywhere, but I went to the parts store and bought a battery-disconnect switch and a fire-extinguisher just to be sure... Fast forward a few weeks, and a friend borrowed the truck to take his date to prom. He calls me an hour later and says smoke came into the cab and the motor cut out whilst driving down the road. I went to have a look, and everything is dead, no electrics whatsoever. I popped the hood, and there are a bunch of burnt and melted wires along the passenger side inner fender coming from (I think) the starter solenoid... ****.... I will get a picture tomorrow, but can wires be individually replaced along with the solenoid? Or will it likely need a whole harness? I'm pretty clueless and my Haynes manual for the truck is super vague in this area

 

You can do each individual wire that burnt up, ( I would take time and do one at a time) I would just check the rest of the wire under the hood to make sure nothing else may have burnt up. And try to find out why it burned up and melted. If you take your time all should go well. Just make a plan and go for and attack.

 

My 74 did the same exact thing and i was dumb and put a 79 wirin harness in it had to change lots of things then i found another 74 one and put it in so i had to change everything back. I would deffinitely reccomend trying to replace every wire where its burnt at, might take forever. Good luck! Lol

 

Ok, after closer inspection in the daylight, I found that only two wires were burnt. I traced then from what I think is the starter solenoid and from the alternator and they both run round the engine bay, through the firewall and to an aftermarket voltage gauge on the dash. The wires are both charred all the way. I disconnected all of the burnt crap and ran a short length of wire from the spliced alternator wire to the solenoid terminal and the truck started first time. I still don't know what caused the problem, but I think the gauge of wire that was used looked a little small, so I think I'm going to replace those wires with a heavier gauge and an inline fuse (don't know what size tho).

 

Today I finally got a chance to work on the truck. As planned, I pulled out the damaged wiring and hooked up fresh 12G wire with a 20A inline fuse, bypassing the gauge on the dash. She started up first time, and I let it run for 30mins before driving it. She ran great for about three miles and then cut out. The new fuse was blown. Do you thing the fuse was too little, or is something causing the current/voltage to spike? I really don't know what's wrong

 

Edit: the fuse that burned out was 30A :/

 

Man i dont know what to think.. i would probably change the sloenoid and see if anything changes, might not do any good at all but they are fairly cheap.

 

I replaced the fuse just because, but it blew straight away, so I have ordered a new solenoid and a voltage regulator. If they don't work, then maybe alternator, then the last straw would be harness I guess... I'm looking at it as a learning experience now as its the only way to keep me from going crazy lol!

 

Haha lol i had them issues and since i didnt wanna cut into anything i just searched till i found an identical wirin harness that was good and put it in. Dont put a newer one in it though, i thought i could make a 79 harness work in my 74 but no lol hope you get it figured out man

 

Your blowing fuses probably because you got a bare spot wire thats grounding out.