Wiring issue causing odd problems.

[nesralyrrej]

Hey all, I did search but maybe I couldn’t hit the right keywords but I couldn’t find this issue here..

My 4.0 swapped '90 just started having a weird issue.

Pulling up to my house the road was rough from the shitty snow, and I hit a bump, the dash lights shut off, the turn signal arrows lit up, and the truck stared trying to stall.. the issue I'm finding seems to maybe be a grounding issue somehow.

Currently the truck runs fine with the lights off, the running lights on they dim and the taillights shut off entirely. When I was laying under the truck looking for exposed wiring or similar I noticed the fuel pump would shut off with the running lights, then it would lose rpm until it almost dies, then it would kick back on and run fine for 10-15 seconds and repeat.

The front lights don't get effected but the brake lights cause the same problem, and if you just tap them the truck with start to shut off until the fuel pump comes back on and it will run fine again until the tail lights come back on.. any ideas?

 

[rusty ol ranger]

Check the cab to frame ground strap. On my 87 its roughly in the catalytic converter area. Not sure on a 90 but pry similar.

 

[franklin2]

Definitely a grounding problem. I don't have a good EVTM for a 1990 that shows the grounding. I know on the larger trucks, they did not use the frame and body as a ground in the rear, they had black wires leaving all the components, spliced together, and the black wire ran up front and was bolted to the firewall behind the radio. Don't know if they had a similar theme on the smaller trucks.

Barring finding the real problem you can add your own grounds. If you found the ground to the fuel pump, you could splice into it and run it up front to the battery negative or some other good grounding spot. That might give everything a new good ground.

 

[nesralyrrej]

The truck is sitting in 5” of ice water currently, I had originally believed grounding issue, so I had ran my big cables to the frame from tbe battery and it definitely seemed better. Hopefully I’ll have time in the next few days to investigate further

 

[nesralyrrej]

Broken ground wire on the drivers inner fender, was hidden under the supercharger intake! Thanks for the help