After looking through this thread nobody really mentioned that the harness plugs into the OEM passenger side headlight bulb plug. Two connectors and wiring are for the 30 Amp relays (high/low beams), that provide the battery power to the bulbs. Two red wires connect the relays to the battery. All in all an easy install with the chassis ground needing to be lengthened for the passenger bulb as per Deadstick's review. Like stated earlier in this thread, using dielectric grease is a good idea on the bulbs & relays to minimize corrosion. The extra OEM connector for the drivers side bulb can be wrapped & tucked away for the same reason.