If you can get the factory harness, i would highly recomend it, the fan wires are part of the front headlamp wire harness assy, comes with relays and fuses for the factory elect fans. You will have to add 2 wires to the factory ecm connector, Also you can take your vehicle to a dealer and he can program your ecm to activate fans. I have done several of these conversions useing oem fans bought from ebay at $250 for the fans, approx $200 for the harness from gm. It is all factory, looks factory and is ecm monitored and controlled, you have high and low speeds. Codes will set if you have a problem with a fan. I have seen other types of setups and many have has many problems, I have done this on my '03 tahoe about a year and half ago, no problems at all. It's a more expensive way to go, but it is more reliable and factory.