pulsating lighs, 86 420SEL
 

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?

Loose alternator belt?

dirty or compromised battery connections?

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!

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

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?!

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

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!)

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.

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.

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