them bones, them bones, them dry bones, . . .
The ground comes from the battery, which is connected to the frame, which is connected to the sheet metal (and the engine), which is connected to the sheet metal, which is connected to the lamp housing, which is connected to the lamp socket, which is connected to the side of the bulb.
If at any point there is not a clean bolt/screw connection, the ground degrades from poor to none. Clean grounds, clean metal, and a conductive anti-oxidant grease make for good ground connections.
Does anyone know what year GM started using wire ground leads?
