Thanks for all the excellent information! I am a total audio novice and have successfully installed a BTA8100 yesterday with very little trouble. I just followed heavyduty's advice given throughout this topic - I used the FAST harness and BTAH cable. I only had to tap in to the red constant wire and the blue-white remote cables at back of harness!!
My only issue now is how to physically mount it since it's in the back of a small hatchback and there is no real wood besides the cardboard thin material that covers the spare tire...
BTW, it sounds pretty impressive. Can't believe how much bass I am getting from this thing!