EDIT I followed your directions ( I think) I just ran a ground wire from a screw on the radio itself to the switch and then ran the parking brake to the switch as well and jackpot! works like a charm, very happy.
I just hooked up my AP2 yesterday. I updated to the new firmware as well I am running on a Galaxy Nexus that I also updated to 4.04 today. Everything seems to be running pretty good I must say although my GPS cable must have fallen off because it's not working and I still have to hook up a switch for video viewing.