Get a copy of the BMW Electrical troubleshooting manual for your car from here Free Phone System Manuals Voice Communications 800 593-6000
and you will be able to track the problem easily.
On a side note, the power window motors in E36's are built like a tank electrically, but the weak point is the motor brushes, which are tiny. 2mm of wear and they are finished, requiring replacement of the entire window motor at $150+! Naturally Brose (the window motor manufacturer) does not supply brushes as a replacement part, but I'm working on it.