300 Sel

[mullet904]

1988 300SEL ~250Kmi. When the key turned to on and the engine not yet started, the oil level, washer level, and battery lights all light up. Starts and runs fine for about 5 min charging normally with system voltage above 13V. Then headlights dim and system voltage starts dropping to about 12V and the car will eventually stall even if driving.

Try to restart, when the key turned to on and the engine not yet started, the oil level, washer level, and battery lights all do not light up. The car starts and runs fine but system voltage remains ~12V and slowly decreases even at high RPM.

I put the battery on change and try to start and the cycle repeats itself.


This forum recommended that I had a bad voltage regulator so I replaced it.

Now everything works and the battery charges but-->I have a 1.4 V, 3 Hz fluctuation in the system voltage measured by oscilloscope that is independent of engine RPM. This also can be seen in the flickering of any lamp that happens to be lit including the headlights. The Alternator waveform is seen on top of this fluctuation and appears normal.


Any ideas?