Okay i know audi swaps the constant and switched lives around so that might be it

Secondly you could try to taking the sled out the car and a 12v supply and run the player that way or try even just running it off your wall wart plugged into the back. Going in through the docking connector might give you more idea.

Also bin hijack incase it is screwing around

One last thing look at the crimping real careful as you might have a dodgey crimp shorting occasionally across the switched and constant lives