Conventional car audio logic is wrong (I wish I could say "but infrequently"). You only need to read some of the forums for a few minutes to see that. I used to follow a pretty good forum for a little while, but even that place found the no-BS people outnumbered by the know-it-all-lemmings. I've also only found one (really) good general car audio site. Can't remember the URL right now, but I know Tony has it in the FAQ.

Here's a link to the BMW info - I don't have individual links to posts saved unfortunately:
http://www.unofficialbmw.com/bmw_e36.html
http://www.unofficialbmw.com/e36/stereo/
http://www.geocities.com/MotorCity/Boulevard/3287/car_audio/stereo_upgrade.html

Wiring specs: http://home.att.net/~ebaines/e36_leads.htm

Note: pin #13 on head unit connector is Illumination and the wire colours for tweeter and mid for the LEFT FRONT are swapped (with each other). And from another doc, the door panels require a Torx 15 driver, not 20. The instructions on Chester's page (last link) for removing rear speakers grills is also incorrect.

Just don't take any of the installation instructions and wiring details as hard facts. Make sure you verify against your actual car and be careful when working. BTW, the stock head unit uses a pentagram key, not a hex key, for its retaining screws. You can (carefully) use a smaller hex wrench to loosen them though. The head unit slides right out afterwards.

Bruno