Search out WDS the wiring diagram system for BMW.

Wiring diagram resources e34:
http://bmwclub.pro/forum/viewtopic.php?t=408

http://www.armchair.mb.ca/~dave/BMW/e34/

You can pick up WDS cheap on EBay, link is broken here but just to give you an idea:

http://www.bmw-planet.net/diagrams/release/us/