[jgravilusmc]

'77 3/4 ton chev. tail lights were dim and now are out (also reverse lights) any ideas what might cause this? i am currently going to clean the ground from the firewall to the block

[poncho62]

Also check your grounds at the rear frame......................Also, on pickups, the harness seems to take extra abuse as it runs outside the body on the frame.

[123pugsy]

There is a connector below the tailgate up under the box. Check to see if its pushed together tightly or if the wires are corroded.

[75gmck25]

Several others have already provided good suggestions that I will repeat, and I have a couple more.

Check tail-light ground wire up under the center of the back bumper where it connects to the frame.
Check ground wire at left taillight (take the tail light assembly out to check)
Check ground wire for the instrument cluster (under the dash, connected to the top of the emergency brake mechanism) - if this wire is missing or loose, it will usually cause a variety of light and instrument problems
Check small ground wire from battery terminal to right fender

Check the pull-apart connector up under the center of the rear bumper. This is where the main harness wiring splits out and goes to each taillight.

Your 3/4 ton truck may also have the towing package or the camper special package. In that case the trailer or camper wiring has a crimped junction at the rear of the truck, just before the pull-apart harness connector I mentioned above. On a camper special the extra wiring goes from there back up front along the frame rail and routes up near the bed area. If this wiring was just cut off (camper or trailer hitch removed), they might have partially grounded the wires together, or to the frame.

If you want to start troubleshooting at the begining of the rear wiring, start where it comes off the fuse box area in the engine compartment. From there you will see a wire bundle that runs down the firewall/inner fender to the frame rail and runs to the rear of the truck. If you can't find the exact problem in your wiring , one option is to just cut the wiring at that point and run new wiring from that point to the taillight wiring junction near the bumper. You can buy color coded wiring bundles from most places that carry trailer wiring. I think they even use the same GM color codes.

Bruce

[Rob Keller]

Check the headlamp switch for melt down.