High Voltage Light On (Temporarily)

I recently took a flight that brought me back in the late evening
hours, and in a hurry, I was a little remiss in my checklist of
securing the plane after shutdown. Landing light, taxi light, strobes,
beacon, nav lights and transponder were all left on, but the master was
shut off.

A few days later, I flew the plane on a local trip, but went to fuel it
up first. During my preflight, I turned the master on, to check the
fuel quantity (even though I dipped the tanks), and to lower the flaps.
I noticed on the startup checklist that I had left these things on,
and shut them all off. This may all be irrelevant, but I just wanted
to state that there was significant load for a short time, before the
engine was actually running.

Flew for about 10 minutes and all seemed well, but I then noticed doing
some 30 degree turns that my voltage light came on. I leveled out and
pointed in the direction of the airport, and the light went off. It
was getting close to dark on this flight, so I thought it was prudent
to go ahead and land and troubleshoot on the ground later. (the light
was still off, at the moment). When I entered a 45 for my approach,
the voltage light came back on, but was off again by the time I was on
final.

Does anyone have any initial thoughts on what the root cause might be?
Any suggestions for troubleshooting?

Thanks in advance!
Todd