Relay Panels - Ground Trigger?

It takes a complete circuit to make a light bulb glow. Usually the hot side is the wire to the socket and the socket is the ground. If you make it a corvette light socket with a return ground wire, you can switch either to make the circuit. Chassis ground is just easier to wire to save wire as the metal chassis is the ground plane, especially in the rear. So the lesson here is to make sure your ground strap is securely attached to the engine AND the chassis with a good star washer digging into the metal.