Ok, I JUST did this so I will try to explain what I did.
1. You have your deck out There are the Left and Right wires + and – then Power (I think white and yellow) and remote Unplug all of them.
2. Pop the fader switch out Cut these wires
Yellow/Red - Left Front Channel
Yellow/Black - Left Rear Channel
Blue/Red - Right Front Channel
Blue/Black - Right Rear Channel
And put that to the audio output on your new deck, Then the speaker out on your deck tie all the ground together.
ok This should all work but you still have the stock amp which need to be bypassed.
3. Go to the trunk and pull the mouse [Censored][Censored][Censored][Censored] back, the amp is on the left side by the antenna.
4. Unplug the amp and cut the plastic connector off. Find
Pair: Black/White and Black/Brown - Right Rear Speakers
Pair: Grey/White and Grey/Brown - Right Front Speakers
Pair: Black/Red and Black/Purple - Left Rear Speakers
Pair: Grey/Red and Grey Purple - Left Front Speakers
And hook them up to
Yellow/Red - Left Front Channel
Yellow/Black - Left Rear Channel
Blue/Red - Right Front Channel
Blue/Black - Right Rear Channel
The 4 above are JUST positive, so for the – on the amp tie them all together. Now I don’t know about your car but I had – wires in my fader, so I tied them together and put the remote wire in them and then connected the remote to the – in the back, so essentially all the grounds from the speakers are tied together. If putting the above wires don’t work you might have to take the speakers out and check what wires are running to them. When I hooked those all up my rear left did not work and I had to pop it out and find what wires were being used.
Now to power the deck, I’m not to sure on this. The + on the stock deck I am told is supposed to switch with the ignition. So Hook that up to the switching power on the deck, and What I did was I dropped a wire down to my cigarette lighter for the constant 12 volt power required for the deck. Theoretically this should turn your deck on and off with the car. But I am having trouble with this.
ALL THIS INFORMATION IS FOR MY CAR and it was all taken from
http://www3.telus.net/baisley/bmw1.htm
Don't quote me on any of this but thats how I got mine going, hope I didn't confuse you too much, if you have any questions PM me. Again im doing this all from memory so something maybe be off, but im 99.999% sure its not