pulsating lighs, 86 420SEL - PeachParts Mercedes-Benz Forum

davestlouis · #1 10-05-2006, 10:50 PM

I noticed last evening that the map light seemed to pulsate in brightness in a rhythmic fashion...tonight the dash lights were doing it, so I stopped, got out, looked around, and every light on the car was visibly pulsing. I parked the car for an hour, got in, turned on the lights, and NO PULSE, just normal lights. What's going on?

raymr · #2 10-06-2006, 08:56 AM

Loose alternator belt?

david s poole · #3 10-06-2006, 09:49 AM

dirty or compromised battery connections?

Johnhef · #4 10-06-2006, 10:06 AM

My 560 used to do this off and on and drive me nuts. I had bought a voltage regulator for it but it stopped doing it before I ever got the chance to put it in. I have no idea what caused it!

Uncle Acky · #5 10-06-2006, 09:41 PM

I would suspect a faulty voltage regulator, (and alternator diode?).

Please check battery voltage, then start engine and check battery voltage again with engine at idle.

I think that more than 14 volts at idle indicates a problem with the regulator and I would not drive the car much for fear of damaging $$$$ electrical components. Beware overcharging as this will create more problems including ruining your battery.

Your best bet might be to have the alternator tested by a pro asap.

Acky

davestlouis · #6 10-06-2006, 11:33 PM

My friendly shop foreman at the dealer seems to think it's worn brushes in the alternator...says he's never heard of such a thing though?!

Uncle Acky · #7 10-08-2006, 08:03 AM

Did he test the alternator output as I mentioned?

Is it overcharging?

It must be tested and diagnosed to be properly repaired.

If it's overcharging, a new regulator will fix it.

*Is there engine oil on the alternator from oil leaking at the front of the engine?

If the alternator has oil leaking on it, it should be re-built or replaced and the oil leak repaired.

My 1992 300E did what you describe, alternator was putting out 15+ volts and was cooking the battery and would have damaged other electrical systems if it continued.

Please deal with it before you have more problems.

Acky

Larry Delor · #8 10-08-2006, 12:36 PM

I thought a bad ground caused lights to pulsate. Check all of your groundstraps (not just the battery ground). (hey...at least that is free!)

400E · #9 10-08-2006, 01:31 PM

Do your dash lights pulsate only when you apply the brake? That's my situation. I learned from another member here that this condition is caused by loose ground strips in the taillight assembly itself.

forcefed44 · #10 06-04-2008, 10:24 PM

Mine is also doing the same situation when the lights are on and at a stop. It annoys me but you can visibly see the lights pulse in a reflection with a car in front of me. Once I'm off, the pulsing stops. My car is charging at 14.2 at idle 800rpm. If I drop the idle to 650-700rpm it will pulse more and lights seem to dim. Does this also spell and Alternator or Voltage Regulator? The belts are new as well as the battery.

Uncle Acky · #11 06-05-2008, 10:48 AM

There are several possible causes, propper testing should find the culprit.
The following should be tested by you or a quallified person/tech with propper equipment.

Faulty or under rated alternator
Faulty voltage regulator
Faulty ground - alternator - engine - chasis - battery
Faulty - too high resistance in feed wire or connection from alternator to junction to battery
Faulty battery

Good luck