The alternator light stays on even though I measure 14V at the battery
poles at 3000 rpm.
Background: 1981 380SE (W 126). Noted a morning a few days ago that the
starter hesitated, like the battery was nearly empty, before turning
the engine over. Was in a hurry driving the kids to school and forgot
about it. Yesterday morning the battery was completely dead. Jump
started the car with an external battery, but after a few minutes
driving the taxomether needle started to behave erratically and
indicated a very high rpm. A few more minutes and the engine died.
Since the battery is several years old I installed a new one and also
changed out the voltage regulator (the old one gave only about 13V at
3000 rpm). Now the voltmeter reads 13.9 to 14.1V across the battery
poles with the engine running at 3000 rpm, but the alternator light
still shines brightly red (it is quite dim at idle).