Many vehicles will have a switched ground that doesn't allow the RetroBright headlights to work right out of the box. This harness is designed to switch the ground back and then the RetroBright headlights can be plugged into this harness. We wanted to expand the great RetroBright experience to the switched-ground vehicles so more people can enjoy the safety and beauty of RetroBright LED lighting. The difference here is in pin that becomes active to complete the circuit, and thus trigger the harness to activate the headlights. In the more common positively switched setups, the ground is constant and the positive pin switches on and off. In ground switched setups, the positive pin stays hot, and the system is grounded when the headlight switch is turned on inside the cabin.