Headlights Dim?

[323BMW13]

On my 2000 323i my headlights will dim when I shift and let of my gas. I have read some other forums about this issue and it said it might be the alternator or battery causing the problem. However, these forums where on other makes of cars so I didn't know if anyone else had this prob. Also, I only have 20k on my car so it seems unlikely the alternator is bad. Any ideas?

[webber]

By the way you explain your "problem" it does sound like the alternator. More specifically the voltage regulator (I'm not sure on BMW's if they're internal within the alternator). This can easily be diagnosed by anyone with a voltmeter. Start the car up and let it idle, check the voltage across the battery terminals should be above 12V, closer to 13V's (can vary as high as 14.5V). Rev the engine up (no need to "floor" it, just rev it) and check the voltage again at the battery as it's being "revved". Again it should be between 12-14.5V's. Turn on accessaries (A/C, Defroster, etc.) and see if the voltage still "holds" to somewhere between 12-14.4V's. The Voltage may vary somewhat while at idle, as it's revved, and also as it's revved with accessories on, as long as there isn't a big drop or fluctuation, then the alternator/voltage regulator isn't the problem. Check your belts, it could be something as simple as a slightly loose belt on the alternator. It's not a battery problem, unless the alternator isn't charging properly. Good luck.