Charging System Gremlin

I have a vexing problem on my 1979 Warrior. The charging system will
shut down in flight at random times. The ammeter drops to 0 and the
idiot light comes on. A recycling of the ALT switch may stop the
problem but it may happen several more times before "settling down".
There is NO pattern to the shut downs. They cannot be correlated to
electrical load, length of flight, weather conditions, time of day,
IMC/VMC, number of passengers, or the color of the clothes I am
wearing. It may not happen for months, then occur without warning.
The alternator, voltage regulator, and battery are all relatively new
(1-2 yrs old).

We have had the FBO look at this several times. Of course it doesn't
happen when its in the hangar during run-up!! One time they said the
field terminal on the alternator was loose and they tightened it down.
That seemed to stop the gremlins but it has cropped up again. The FBO
now reports "no problem found".

Of course if the charging system shuts off and stays off, this is what
I would call "bad news"...especially in IMC. So far its just been an
annoyance and my pulse no longer jumps to 150 when I see the charging
warning light come on.

Any ideas on what could be causing this?

Thanks!!!

--Jeff