Electrical problems with lights

[Rev_S_Jones]

I recently bought a 92 GMC Sierra with a 6.2 Detriot diesel. I live in Georgia but the previous owner lived in Canada. He used the truck as a snow plow exclusively his property so there is little to no rust damage on the truck. For a 31 year old truck, it is very clean! The truck also has a light bar that I have struggled to get running properly and at one point had an auxiliary fuel tank. I plan to eventually get rid of all the aftermarket wiring and put a cleaner system in to run the light bar.

The issues I'm having are 1) headlights and running lights dim and shutting off within a minute after turning on my high beams, 2) left side blinkers not working when headlights are on, 3) reverse lights not working at all.

All my bulbs are good. I've replaced the headlight switch, tail light circuits, neutral safety switch, and reverse light bulbs. I did notice on the neutral safety switch that ther are 5 prongs but I only had one harness to hook up to it (the top one with the blue and green wire).

I thought about checking the grounds but I don't know where they are located except for the tail light ground at the rear of the truck. I think it's also possible that some of the aftermarket wiring may have something to do with it. I haven't checked the high beam switch.

 

[Rev_S_Jones]

Update:

I unhooked the trailer harness and the turn signal issue was immediately resolved. I also unhooked the harness for the high beams and found and excessive amount of dielectric grease inside. I cleaned it all out and just sitting in my yard idling, the headlights seem to be operating properly. I haven't done any extensive driving so I don't know ow for certain if these really fixed the issues.

There is a switch at the very bottom of my dash that toggles the running/headlights on and off. When I was running the truck and the lights, the wires at the base of it felt very hot to the touch but nothing smelt like it wad burning. I'm not sure if this is normal or not.

I'm thinking that my reverse lights might have something to do with the wiring under the dash for the aftermarket light bar and fuel tank.