In article ,
(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

from the Cherokee hints & tips, there are several potential causes.
Most are related to loose connections or corroded connections (the
connection heats up, becomes open, cools off and closes). The time
I had a bouncing ammeter, it was caused by a bad master switch.

Checking and cleaning all the connections is the cheapest first step
in troubleshooting this (assuming you are doing it) rather than trying
to isolate the problem by swapping out the ammeter, regulator, or
alternator.

--
Bob Noel