I installed 2006 E-fans on my 2001 GMC Truck Forum. Web  Here is a wiring diagram of how the fans are factory wired on the 05-06 GM trucks. If you have an 03-04 truck, then you will wire it.

WebThe small GREEN wire from the fan needs to be inserted into PIN 42 on C1 and the small blue wire will need to be inserted into PIN 33 on C2. Using a straightened paperclip push.