Hello, our 1991 300e did some wierd things when my whife drove to work yesterday.The dome light and fasten seatbelt light flashed for about ten minutes.The radio also would not power up.When she drove home,all was normal.I took the car for a short drive and all was normal.I was thinking possibly the alternator brushes could be going ....any thoughts???Thanks, DAN

Sure sounds like it.

Measure output at the battery terminals with a voltmeter. Should be 12V at rest and 13.5-14.4V with the engine running (no accessories)...

...less than 12V at rest indicates the battery is low. If you get nominal readings while the engine is running, it is definitely the battery. If it's too high or too low, it could be brushes or the voltage regulator...

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

Thanks for the info. I checked battery voltage :engine off=12.56 volts,engine on,accessories off=13.89volts.This is within spec I believe.I removed regulator assembly and found the brushes worn down to the little "R"that is stamped on them.Prehaps they are at their maximum wear limit and the cold ambient air temp that morning (45 degrees)caused intermittant contact til things warmed up.Just a theory since the car has run fine since.Iwill replace the regulator at my earliest convenience.138k miles is pretty good service from this unit!Thanks for the feedback,Dan

You are within spec. However 13.89V seems a bit low with no accessories...consider that if you run everything full tilt your alternator is probably giving the battery very little charging output.

I lost my voltage regulator at around 125K...you did well with yours.

When I lost mine, it was overcharging, and I was seeing 17.5V at the battery...which was furiously venting out sulphuric acid vapor!

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

Well I put the voltage regulator in today and voltage is@14.2 without accessories.I bought it at the local benz dealer cause I didn't wanto wait.I was dismayed to see CHINA stamped on the thing.Also had trouble installing because the ceramic insulator was about .015"taller than the old part .Had to really press to get it to line up with the holes.I hear benz is moving E&C class production to Bejing.I guess part sourcing is going there also.How sad.I've seen very few products produced there that are of excellant quality...Just cheap copies...Pretty bad we can't get guality parts at the dealer any more!Sorry about the rant but I see alot of this and never expected benz to go down this perilous road.Thanks for the help,Dan
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