Danny,
Welcome to the Stovebolt..I think half of Texas is on board.
This has always a tough concept for me to grasp. A picture of a '58 Stepside shows two single light assemblies in back. I think this means each housing has a single dual element lamp in it. The lamp would consist of a large stop filament and a smaller tail filament.
Wouldn't the base of each bulb be the common ground for both filament to housing/bed/frame. If this is true, then having the taillights function would mean the ground path is good. Does this sound reasonable.
If there were two housings in back of the truck, that would mean they would both have to have identical ground problems.
Finding ground through a nearby filament is known to happen, but I can't see how it would work in this scenario.
I would pull the lens off the lights and see exactly what the bulbs were doing under each condition. This might give you some direction.
Stuart
