My AMP meter in my old Arrow would bounce as well only when the strobes
were turned on (Whelan Comet Strobes) otherwise it was rock solid.
Maybe you have a current drain, or a loose connection someplace?

Leo wrote:
Usually the hand on my ammeter bounces for a few moments while taxing
and then settles down at about 20 amps. Yesterday it continued to be
erratic with a few calm moments with the hand indicating 10 amps. The
ammeter has 1976 stamped on the back. Do these things ever wear out?
Is there any way to bench test one? I need a few opinions, what is
the most likly culprit - ammeter, regulator or alternator? Thanks Leo