I assume you mean the red LED Overvoltage light on the passenger side.
In my 172M, when it came on, it would latch on until the master was
turned off and back on again. Is that what you are doing in flight?
Or maybe you have an intermittent in the indicator too?

FWIW, for a while though we messed with grounds at and around the
voltage regulator with some success. In our case the Overvoltage
sensor was detecting at too low voltage and was finally replaced.
Problem solved.