Electrical Gremlins ready to burn down the truck

[Knakai767]

Apologies if this is not the correct area, please move if needed

1991 1/2ton 350tbi 700r4 4x4

I've owned this truck for a couple years now, beginning about a week or so ago the truck would randomly have this issue while driving where everything would spazz out and the truck would try to die. and by spazz out I mean the radio would make loud interference like noises, the parking brake light would come on, and the tachometer would bounce around a little bit, volt meter would drop. This would only happen for about a split second or so. It was fairly rare, I did notice it happened more on bumps.

I figured something may of been loose. I checked my battery, got it mounted a little better than it was. it is fully charged, positive battery terminal was loose, tightened it back up. Checked grounds and power wires, all was good. moved on.

a day or so later the truck completely shut off while driving, the radio made the loud noises, and would not shut off even after switching the ignition off. It didnt shut off until I pulled it out and disconnected it. However, there was no power to anything except for headlights and glovebox light. No windows, HVAC, gauges, starter, nothing. I left the truck in a parking lot.

Came back to it today with some tools. I found that the fusible link. (3rd from left, black one in front) was blown out. replaced, as soon as I touched the ground side battery terminal to the battery it sparked and popped the link again. I replaced the link with a jump wire of the same gauge just so I wouldnt go through a thousand links finding this thing. I took out all of the under dash fuses, still was shorting. I went ahead and disconnected the ignition switch off the column, even though I knew it was new. Who knows. Still pops. Okay, so I'm looking around the truck trying to find where this short can be, disconnecting anything that looks like it may have been hot at one point. I went over the power and ground wires again, nothing wrong there. It pops off like theres just a nice big fat power wire bolted right to ground but I am not finding anything. I came back home, I decided when I go back to it tonight I can d/c alternator to eliminate it, and d/c the main harness to the firewall. if its still not working though I am really out of ideas other than going around to all over testing for power and disconnecting everything until it stops. I feel like the system is pretty simple, I just cant think of anything else to look at. Quick help is greatly appreciated so it doesnt get towed off

 

[Wade]

If you haven't already, check all the grounds, often times it is something simple.

 

[Schurkey]

. I found that the fusible link. (3rd from left, black one in front) was blown out.

Get a REAL service manual with wiring diagrams. Trace that fusible link in the diagram, find out what it powers.

 

[edonwheels]

Mine was doing the same thing it was a power wire from the battery to the trailer brake. The header melted a spot on the wire and it would only do it on rough roads.

Sent from my LGL164VL using Tapatalk

 

[Eveready]

Power windows / locks? Might be the positive battery line to the door since the switches work by providing the ground. Worth checking the wiring going into the doors as that is a wear point. Does not sound like a ground with that link going. It IS grounding but as a short, not a factory planned ground.

 

[Supercharged111]

Don't rule out aliens. This sounds like some Men In Black ****.

 

[Mike Duckworth]

Check the wire bundle that runs across the back of the firewall , I had a similar problem and the plastic strap that holds it up broke from years of heat and it fell down on the exhaust manifold and burned the corrugated plastic wireway and when it got hot and you hit a bump the bottom wires would go to ground. Good Luck.