I have the same issue although I have a PCM for less harness which only uses 2 relays and then leaves you with the dark green wire hangin unattached which you are then told you can hook up to a manual switch to turn fans on with.. I don't want this as the AC doesn't work now when the truck is not up to temp and sitting in traffic not moving air across the condensor.. So I found the truck harness green wire and now I need to make them work together.. THe problem is the truck wire puts out 12+ when the AC is on and the harness wire works when you ground it.. SO what type of relay etc do I need to get this to work? I looked at the diagram attached in here and have no idea what to do with that info?

 

You can get a standard 12V relay from any parts store. You will turn the a/c wire into a switch to connect the green harness wire to ground.

On the relay, connect either pin 85 or 86 (doesn't matter which) to the a/c wire. Connect the other to ground. What this does is create a switch that turns on whenever there is a voltage difference between the two pins (i.e. when the a/c is on and the a/c wire has +12V).

Connect either pin 30 or 87 to your green harness wire and connect the other to ground. This is the switched circuit. When the switch is engaged (a/c on), your green harness wire will connect to ground and the fans will come on. Make sense?