I am new here and have a 2004 gmc envoy with factory navigation. I just purchased a used factory flip down rear dvd that came out of a another envoy. Can anyone tell me what wiring harness I need to hook this up? Also can anyone tell me how to go about getting this hooked up? I have the rear audio controls and have read that some of the vehicles come with the wiring harness already. I looked in the headliner the best i could but didnt see any harness.