Could be the master switch or it could be the master contactor, it's
usually located right next to your battery box. Replace the contactor
first as it's very easy to do and about a $20 part.

three-eight-hotel wrote:

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?


Correct... it's the red LED, however, mine is on the pilots side. I
did not have to turn off the master though. It came on the first time
when I was in a constant 30 degree bank, and went off by itself.

Something else just occured to me... A couple of months back, I
switched on my master switch, and nothing??? I switched it back off,
and switched it back on, and it worked fine. A friend of mine said
that my master switch was probably on its way out, and that I'd
probably be replacing it soon. It happened about two more times after
that, but has been working fine ever since. Is there a potential
relationship here, or are these two separate issues? Was there
something else going on besides the master switch starting to fail, or
could the failing of a master switch be tied in, some way, to cause the
voltage LED to illuminate?

Best Regards,
Todd