On 3 Dec 2004 14:08:35 -0800, (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

99% chance the ammeter is ok, as are the VR and alternator.

Two most likely causes:
1. Bad master/field master switch. Contacts heat up, break contact,
cool, contract, and begin the cycle over again.

2. Intermittent resistance in the path from the main voltage bus to
the voltage regulator. The resistance can caused by corrosion of
failure of any one of the following components:
2a. Field current circuit breaker
2b. Connection from field current breaker to field (master) switch.
2c. Field (master) switch
2d. Connection fom field master switch to OVR
2e. Connection from OVR to VR

If your plane is a 1970s Warrior - these components are approaching 30
years old. Replacing the switch, circuit breaker and wiring is cheap
insurance against electrical failure.

-Nathan