These links may be of use to you:
http://forums.bimmerforums.com/forum....php?t=1111254
Check Post #3 for colors. The thin white wire is for the power antenna if you have one and the switch for the amp. It has to wired up to the power antenna cable on an aftermarket radio. You will also need to take the two thick brown wires which are for the common ground system and stick them to any metal part of the headunit. My Blaupunkt aftermarket one had the stock system where the two grounds attach to a screw post. Also note that you should tie up all the (-) speaker wires together and not attach them anywhere. The common ground system does not require for them to be wired, with the stock amp that is.
http://web.archive.org/web/200704081...ldWire_big.jpg
http://web.archive.org/web/200704080...eo/Old_big.jpg