to get from the outer surface of the tail light bulb with original tail light housings on a bus up to 1971 to ground – the chassis, which is directly connected to the negative terminal on the battery. First, the ground current leaves the outer, round surface of the bulb and into the cylinder that surrounds it. That’s one interface. The cylinder is  crimped around it’s circumference to the the reflector/housing. That’s another interface. But there’s also a small tab […]