This is what I started with.  At one point there was an aftermarket stereo of some sort in here, but the previous owner removed it.  And none too gracefully either.  So the first step was to figure out where everything went.  And fortunately a buddy of mine had harvested some adapters from a junk yard that fit perfectly onto what was there, so that gave me some wiring colors to work with.

​What I finally figured out is that these wires all go to an amp mounted in the trunk, and from there goes out to what appears to be five million speakers.  But connected to the radio are no negative wires for the speakers.  So I just capped those off when I installed it.  

What confused me to no end was the light blue wire.  It was supposedly coming from the amp, but when the key was on, it was hot.  Eventually I connected it to the remote wire of the stereo and voila!  It worked!  It was easy enough to run the aux audio cable and usb cable to the glove box, since you can just reach your hand through it and pull them through.  ​I haven't decided what, if anything, I'll do with the microphone for the phone.  Newer bimmers have a microphone in the area above the rear view mirror in the headliner, so it's an idea.  We'll see.