My headlights bright&dim w/engine speed...symptom of..?

[RobPatt]

noticed coming home tonight....confused whether it's alternator or voltage regulator and the interplay between the two... or something else? Thanks. -Rob.

[Kalevera]

Could be the battery. If no other accessories are acting weird, I'd check that first, then the voltage regulator. Good luck!

[Tiger]

Poor Ground Contacts

[ryan roopnarine]

the voltage regulator is 1/2 of the alternator, ie makes the current and stabilizes it, the bearings, windings and diode plate make the ac, and straighten it into dc. does it get brighter with higher revs? that might be the regulator portion of the voltage regulator (as opposed to brushes). you can always take it to autozone and see if they can rule out which half (battery or alt.) is doing it, then figure out what you have to do from there. i take it it is still driveable? hopefully if it has something to do with your alternator, its just the regulator, i don't think that anybody here has come up with a solution for a diode plate problem that will work in a regular e34 alternator.

ps....pls disregard half the stuff i said above. it sounds like your battery is dying. how old is it?

[Javier]

variations with a voltmeter, at battery posts, battery clamps, and jump start post to car chassis ground. This may help to understand it.

Javier

[Mobius]

Does it spin over nice and fast when you start it - or does the starter seem like it's straining?

It's probably just a dying battery - exacerbated by the colder weather.

If it's not of the maintenance-free style, check the water level (though it probably is too late for that).

[bill g]

Sounds like voltage regulator to me. But check for good engine ground ie. the cable from engine to body.

[RobPatt]

just w/higher revs the lights get a little brighter. After revs when the speed/idle dips a bit low the lights get dimmer for that second, then go to normal... rev up, they brighten, idle dips, they dim, then normal, and repeat.... no other signs... thanks, will check volts at grounds/batt/etc as mentioned...and see what an autozone place may be able to do. -Rob.