I fought the same problem for a couple of months on my 2000 X5, it turned out to be the final stage resistor for the climate control. I was clued in here when a member mentioned a running fan with the key off, I heard the same thing one day. I bought the part on ebay for around $60 and followed instructions posted here, problem solved. During my troubleshooting I connected a multimeter between the positive terminal and battery cable and measured the amp draw after all the interior lights turned off. I compared that to my other cars and they were all about the same with the alarms and all, about .5 amps if I remember right. You might want to try that and see what you get. Good Luck!