BMW Repair: battery keeps going dead, volt ohm meter, sleep mode

Question
My car wouldn't start this morning at all. It doesn't make any sound when I try to start it. It cranks up when I jump it off but when I turn my lights on my radio cuts off then my car. I purchased a new batter and an alternator and the battery still won't hold a charge. Could it be my ignition switch or something?

Answer
Something is draining the battery.

If you have a volt-ohm meter, put it in line with the battery and look for a drain.

I know that late 90's BMW's have a shut down sequence, where upon shutting everything on the car down, there remains a relatively high drain on the system for about 10 minutes, then a "sleep mode" kicks in, where all the computers quit talking with each other.  If your car isn't going into, or staying in, this mode, the battery will drain in less than a day.

Tracking this kind of issue takes a lot of time.  With the meter, try disconnecting half the electronics at a time, and looking for the problem.  Then half of hte half, and again, and again, until you find it.