Hmmm. I did post about this years ago, but damned if I can find it.
I remember a lot of figuring out what wires were what... and that it still needs to "think" the head unit is active (sound stops for a few seconds every time the cd ends and restarts - always meant to put a much longer cd in there, but never have - wonder what it is that I play over and over again that never gets listened to).
I'll see if I can find photos from the time if you are serious about doing it...