300E W124 engine.
I am guessing that the voltage regulator (VR) is bad.
Thinking of taking it out and testing it at Auto Zone or pep boys.
is ti hard to replace the VR? How about to take out the alternator?
I was also thinking to change the poly V belt too?
Do I have to take out the fan for changing the belt?

thanks
ACM

The voltage regulator is bolted to the back of the alternator and is easy to replace. Go to fast lane and check out the photo so you will know what to look for. Odds are a new one will fix your problem.

Did you check the voltage across the battery with engine running? If you get 13 volts, the alt. is OK

If you get 13.0 v running with either a cold or warm motor, somethings not up to snuff. It's been my experience that once you start seeing < 13.5v on a warm motor at idle, it's time for brushes/alt/etc. Cold motor voltage reading should be more like 14.0v or better...up to about 14.4v max.

My 2 cents.

__________________
'91 300-SEL

yes the voltage is low about 10 Volts.
So most likely is the voltage regulator.
Anyway to test the regulator it self?
Auto zone said that they can not test it by itself
thanks
ACM

Hi,

You've tested the regulator yourself.
10 V is the answer. It's fried
The gentleman from Alabama has suggested an excellent solution.
This is one of the easiest and most instructive repairs,have fun!

Brushes are likely worn down to nothing. New ones are 1/2" long. Pull the old ones and see what you've got.

__________________
'91 300-SEL

. . probably just the brushes. Try this; with engine running, tap the back part of the altenator with a small hammer. If the voltage jumps to 14.x volts w/ engine running, it's the brushes.

If the alt was fried, you would a faint glow for the battery icon in the IC.

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

Badly worn brushes will also cause this.

__________________
'91 300-SEL