The lamp socket to the housing and the housing to the car. Power runs from the switch through the wire, into the socket, into the lamp, out of the lamp to the ground tab on the socket, from the ground tab to the housing, from the housing to the body, from the body to the ground wire to the engine block, from the block to the neg[-] post of the battery. Sometimes the ground strap from the body to the engine block is missing and the ground finds it's way through the mounts and other fasteners into the frame and to the block and eventually to the battery. Quite a few electrical snags with these cars are grounding problems.