I read about this issue somewhere else but I can't seem to find the thread anymore so I am posting one of my own.
I installed my X920BT into my 2007 Mustang GT last weekend. I did it myself with the appropriate PAC harness and I added the GEX-P20HD as well. I also did the hack moving the mute wire one slot over and grounding it with the parking break wire, hack works fine. I took my time on this install, a good 10+ hours triple checking all connections with the instructions, soldering and shrink wrapping them so that everything would be perfect.
Day one everything worked great and I s