: Headlights and instrument lights alternate brightness

05-12-2009, 10:28 AM

I'm a new 1979 320i owner and I've noticed that my headlights seem to go back and forth from slightly dimmer to slightly brighter (not high beams bright, just a little brighter). It reminds me of when I see some motorcylces drive by with a headlight modulator. My instrument panel seems to do the same as well. The rate of "flash" is probably twice per second.

I've searched the forum and didn't see any similar post. My first guess is an alternator problem but I'm a novice at mechanical / electrical work. I'd appreciate any advice. Please let me know if I've let out any important information.


05-27-2009, 10:18 AM
does it seem to vary with the engine speed? Mine will get brighter with a faster engine. also at night does the battery light on the dash seem to glow?

06-15-2009, 09:32 AM
Sorry it took a while to respond, I've been out of town with work for a few weeks. To answer your question, the flicker in the lights seems to happen when the car is idling a little higher just after I start it or when I push on the gas pedal a little bit. When the car slows to it's normal idle (I'm not sure exactly what RPM because my tachometer doesn't work) shortly after the engine is started it seems to stop. The alternator seems to work fine since I drive the car an hour and from work everyday and it never conks out. The battery seems to be holding a good charge but I've tested it and the voltage with the car running fluctuates between 12V and nearly 15V so I'm guessing the voltage regulator in the alternator might be going.

You mentioned that yours get brighter and remain brighter as you press the gas? I wonder if you might have a similar problem with a slighty different symptom. As far as my battery light is concerned, I haven't noticed a glow but I'll check it out next time I drive at night.

07-25-2009, 03:54 PM
I have heard that a diode in the alternator can cause my symptom on a pulsing battery light. do you have a aftermarket radio installed by chance?