I went through two brand new voltage regulators on my '68 F250, both the old fashioned, bulky, mechanical type. Turns out NAPA offers a "solid state" (i.e. transistorized) voltage regulator which worked and still works. You can immediately tell the difference because it is a much slimmer unit than the original.

This probably doesn't help the original question, as I don't know if your alternator is internally or externally regulated, but it seems to me that there are some poor quality mechanical regulators out there. Both of my bad units would overcharge to the tune of 17 volts or so. Part of the reason why a volt meter is so much more useful than an Ammeter in a car.

Kevin

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'85 300SD