For the stock 10-speaker, 200watt stereo in the E36, the following info gives you the wiring diagram to the factory amp behind the drivers side rear wheel well.

10-speakers
2 tweeters in front doors
2 midrange in front doors
2 woofers in front kickpanels
2 tweeters in rear deck
2 mids/woofers in rear deck

Amplifier
2 Connectors:

1)

 +-|_|------------------------|___________|--+
 |  1  2  3  4  5  6  7  8  9  10 11 12 13   |
 |  [] [] [] [] [] [] [] [] [] [] [] [] []   |
 |  [] [] [] [] [] [] [] [] [] [] [] [] []   |
 |  14 15 16 17 18 19 20 21 22 23 24 25 26   |
 +-|~|------------------------|~~~~~~~~~~~|--+

1 - brown/orange right rear - (from radio)
2 - blue/black right rear + (from radio)
3 - yellow/black left rear + (from radio)
4 - brown/orange left rear - (from radio)
5 - n/c
6 - n/c
7 - n/c
8 - blue/red right front midrange +
9 - blue/brown right front midrange -
10 - yellow left rear tweeter +
11 - brown left rear tweeter -
12 - blue right rear tweeter +
13 - brown right rear tweeter -
14 - brown/orange right front - (from radio)
15 - blue/red right front + (from radio)
16 - yellow/red left front + (from radio)
17 - brown/orange left front - (from radio)
18 - n/c
19 - n/c
20 - n/c
21 - yellow/red left front midrange +
22 - yellow/brown left front midrange -
23 - blue/black right front tweeter +
24 - blue/brown right front tweeter -
25 - yellow/black left front tweeter +
26 - yellow/brown left front tweeter -

2)

 +------\/----\/-------+
 |  7  8  9  10 11 12  |
 |  O  O  O  O  O  O   |
 |                     |
 |  O  O  O  O  O  O   |
 |  1  2  3  4  5  6   |
 +---/\----/\----/\----+

1 - red/white battery
2 - white remote turn on
3 - brown ground
4 - n/c
5 - blue/violet right rear woofer +
6 - blue/grey right rear woofer -
7 - blue/white left front woofer +
8 - blue/brown left front woofer -
9 - blue/red right front woofer +
10 - blue/brown right front woofer -
11 - yellow/grey left rear woofer +
12 - yellow/black left rear woofer -

Another view of pinouts