Backup Lights Issue

[Anonymous]

The previous owner ran a separate ground off the driver's side B/U light. If the ground for the rest of the rear lamps is connected as well as the B/U ground the B/U lights do not work. If only the B/U ground is connected the B/U lights work but are dim and some power appears to bleed to the tail/brake/signal bulb (very dimly lit). There are no issues with the tail lights, signals, brake or markers with only the lights grounded or both the light and B/U lights grounded. Any help is appreciated. The vehicle is a 1980 el camino.

 

[Garage Hound]

Avoid going backwards?

 

[Doober]

It would probably be a good idea to pull down that entire rear section to see if everything is still wired like it should be. If a previous owner added a ground, there's a chance they may have changed something else? That doesn't make a lot of sense for the backup lights to not work at all if they're both grounded.

What I would do if it were mine is take all the bulbs out of the housings, and drop the harness a couple feet from the lights on back, so there is some room to move it around. I'd pull all the old plastic tubing off the harness back until it looks unmolested/semi clean and take a good look at all the connectors, looking for broken wires or cracked insulation. If the insulation is cracked it was likely letting moisture in, and there's a chance the wire may have become corroded and broken inside the insulation.