This harness is the main harness which most other harnesses plug into. It contains the fuse block and connectors for headlamp switch, ignition switch, dimmer switch and firewall connectors. This is a high quality harness made from the original factory blueprints for an exact fit. We believe this is the best harness available. For trucks with automatic trans. unplug the loop and plug in to your neutral safety switch and for trucks with standard shift trans keep the loop installed to complete the circuit.