I posted a few pics
here. Didn't find the whole deal yet, unfortunately. I KNOW I have a complete late model e30 harness somewhere.
The wires are very simple. Some BMWs don't have speaker negatives, they're all on a floating ground (Brown/Orange) IIRC. Don't quote me on there, trying to recall them from memory.
Constant +12V - Red/White
Switched +12V - Purple/White
Ground - Brown
Isolated (speaker/chassis) ground - Brown/Orange
Pwr. Antenna - White (small gauge)
Illumination - Yellow? (might have been gray - it's the other small gauge one)
Front Left (+) Yellow/Red
Rear Left (+) Yellow/Black
Front Right (+) Blue/Red
Rear Right (+) Blue/Black
This likely won't be a problem for you. But FYI, I had to tap a more powerful "battery/memory" (constant +12v) on my car when I upgraded...the stock BMW connection doesn't provide enough amp headroom for newer head units with integrated pre-amps. I ended up pulling battery power off the 4-way blinker (hazard) switch in the button panel above the stereo for my Blaupunkt. Can't miss it, it's a huge red wire...might be 12 gauge.
I also almost forgot...the premium sound system has a dedicated amp/crossover in the trunk and a different wiring harness. Earlier e30's with this system have a fader switch wired into the harness as well.