alternator pulsing high while charging

[EClancy]

92 cdt, 4x4, auto, 116kmi.

i installed an external voltage regulator, as to get around a wiring meltdown that was not my fault. worked great for a while, charging at a steady 14.2+- volts. started truck friday, charged as normal for a while, then aftermarket voltmeter and factory batery guage started jumping rythmically at the high end of the range. interior light and underhood light would also pulse. a check w/the multimeter revealed a steady pulse of 14-16v.

went out and bought a new VR, just to rule it out. cleaned grounds down to bare metal. truck would charge at 14.6v-15.1v, pulsing in a steady alternating pattern. truck light had a barley noticable pulse, in fact, i would not notice if i was not looking for it, but again, the multimeter at the battery does not lie. factory guage still jumping around at high end of guage.

Tested alternator for AC voltage between positive battery terminal and alt case. got a steady 27 or so volts.

any ideas on what my issue is?

[BobS]

If your alternator is putting out AC volts instead of DC volts that would indicate you have a partially shorted rectifier in your alternator.