This harness is originally intended as an upgrade for earlier GM trucks with a mechanical fan to now run (05+ GM truck) dual electric fan that is controlled directly by the ECU. Your computer will need to be flashed to add the fan control. Wired with 05+ GM truck fan plugs Waterproof relay connections Dual Fan Control - This is a three relay system. Both Red & Blue ring wires with ring terminals go to power. NOTE: If you are using one of our standalone harnesses in conjunction with this, the wires will need to be extended to reach the PCM/ECU.
