"bill" wrote in message . com...
Well, I can tell you what it usually is. I use to have a Cessna shop back
in Michigan and most of the time this was cause by the failure of the
overvoltage protection relay. In fact Cessna has a service letter on it
that requires you to place a capacitor in line with it because this relay
has a tendency to kick off too easily as it gets older. I don't recall what
year Cessna incorporated it into manufacturing but it was in the early 70's.

It shows up the way you described, occasionally at first and then more often
until finally you won't be able to recycle it back on. I had to replace one
on my 172 last year, same symptoms. It's located in the wire bundle behind
the CB panel on the pilots side on most models. A cylinder about 3-4 inches
long, 1 inch in diameter with 3 wires.

You can get them from Cessna or for less money under STC from Chief and
other suppliers. They're listed on their web site.

A bad grounding of the ground lead from the overvoltage relay
can cause the same problem. They're often connected to the park brake
bracket, which gets pulled and flexed and thngs eventually come loose.

Dan