Here is the ground signal hooking to the courtesy lamp circuit. This circuit receives a ground signal, which energizes the relay and send the power where it needs to be (lamps): Mirror heat/defrost One thing to note: the mirror heat is on the same circuit and the rear window defroster. I don't have a rear window defroster, but it seems that the wiring is included.For the mirror heat, I wanted a factory wiring solution as well. The wiring harness to the mirror already had the this wire included (good thing). I need a way to turn these things on: I could install a switch, but I didn't want that look. So, since the rear defrost is the same circuit, that would be a great way to turn them on - Just by a new HVAC control unit that has the rear defrost switch on it. Now, this is the more expensive way to go, but, by far, the easiest. I also found out that I needed the relay for the circuit as it was not included on the underhood fuse block. So, I purchased a new HVAC controller and a relay for the circuit. Can you say, "Plug and play" - it was that easy. Just push the button and mirror defrost is activated - the great part about this: It is the factory installation and it uses a relay timer in order to turn the circuit off (through the BCM, I presume).