Haven't posted here in quite some time, but I just wanted to provide some helpful info that I learned this week.

I started up my car the other day and discovered that my seatbelt light did not go out when I buckled in. Then I noticed that my aftermarket XM radio (XM Commander installed via CD changer) was not working. It was picking up satellites, but the music wasn't playing over the speakers. On the drive home, I soon found that my dashboard illumination did not come on when I turned on the headlights, and the turn signal indicators on the dash did not light up either. Also, the clock display on the instrument panel was OK, but I could not get the radio display to switch to clock mode. My cruise control buttons on the steering wheel worked, but the radio buttons on the steering wheel did not work. Once I got home, I played around with a few more things and discovered that my convertible top would not go up or down either.

I called a local mechanic and he said to replace the battery first. So I did that and things only got worse. Once I reconnected the new battery, my radio only displayed "-DISABLE-" and my power windows ceased to function.

I spent hours and hours Googling the internet for answers, and found this tidbit on another BMW user group website:

Electrical systems going whack?
There are two problems that affect all of your electrical systems. Symptoms include steering wheel buttons not working, turn signals or gauges not working, radio not turning on, etc.

The most common cause is a failed device on the iBus: try unplugging your cd changer, ipod adapter, satellite radio, etc.

The second most common cause is simply a bad battery.

Since I had already tried the battery, I tried unplugging my XM radio from the CD changer port. This did not help. I had one more option. Two years ago, I bought one of those iTop modules from Bavarian Auto (module built by TVonNAV, which has since gone out of business). It died during this past summer, I suppose 2 Texas summers was too much to ask from it, but I just left it in anyway. What harm could it cause, right? Well, I took it out and all my electrical problems went away. Car is as good as new.

I hope that this can help someone else in the future. God knows that this forum has helped me a lot over the past 4 years.