headlights dimming

My 1994 740iL (85k miles) runs fine, however when the transmission is downshifting (as the car slows) the headlights dim momentarily then come back to normal intensity. Normal cruising at steady speed – no problem. At first I suspected the alternator, since the headlights exhibit the same dimming when the car is in reverse. (backup lights taking the juice?) The puzzling thing is I don’t seem to be losing the battery charge, and the dash lights, fan blower speed, etc are not affected. Has anyone had a similar problem, or some idea of the cause? Thanks

Hi!
Check your voltage regulator.
Try test 9 on your OBC...it simulates a voltmeter.
Look if your voltage varies a lot in idle, while runnin and before starting.

Hope this helps.

bmwstyle 1988 730i e32

Thanks, OK I'll give the test a try.
Where is the voltage regulator located anyway, is it attached to the alternator?
muleman

Hi!
Check your voltage regulator.
Try test 9 on your OBC...it simulates a voltmeter.
Look if your voltage varies a lot in idle, while runnin and before starting.

Hope this helps.

bmwstyle 1988 730i e32

When was the battery replaced last? If it has been a long time these cars do funny things when the battery gets old.

Thought of that one, two weeks ago. No luck. Also replaced the LKM which was to no avail. Could it be that the idle is too low? (500 RPM)

When was the battery replaced last? If it has been a long time these cars do funny things when the battery gets old.

Have almost the same issue on a 1988 735iL the headlights just cuts out but the fog lights stays on. SO I had to enable the high beams that really is not a good thing. But when click to low beam the lights sometimes comes back on. Mostly happens on a damp or wet day. So in my case something could be grounding it.
They say that the relay switch does not last forever but they are expensive to replace. I wonder if the wiring is worn out. Don't know it has a mind of its own.
So I hope that when my lights shuts of and the fog lights stays on hope that that is not illegal a reason to be pulled over. I'll research some more on this.