Hi All,

It’s an '81 242DL B21F with external regulator. The alternator has been changed several times through out the cars life (I've owned it since '86) and it's the original style small 70-80 Amp (?).

Yesterday my voltmeter suddenly showed 10-11 volts after driving for half an hour. The Batt light never came on but it works when I just turn the key on.

I measured at the battery and the alternator's output terminal and got about 11 1/2 volts for both with the engine running. I then tried removing the regulator and jumped D+ to DF at the plug. This gave About 15 Volts at the battery with engine running. I replaced the regulator with a PnP unit, which seemed to fix it. My voltmeter read about 13 Volts. The next day, after a short drive, my voltmeter again dropped to 10-11 Volts.

So, is the alternator blowing regulators and why isn't the Batt light coming on?

81,

I don't believe you are killing your regulators. More likely, you are chasing a lousy connection. The warning light does a good job alerting you to some faults, but not all faults, which you would have to agree describes the majority of posts you read on the subject here. In other words, if the light comes on when you are driving, expect a charging fault, but if it doesn't come on while driving (and does during lamp test), the inverse is not necessarily true.
--
Art Benstein near Baltimore

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