C99 Captain reported confusion over the system operations for the Master Caution Annunciator. The Captain elected to make a log book entry after reaching destination airport.

Narrative

I started my day in ZZZ and did my preflight and did not see any discrepancies with the airplane so I was released and did the run-up and departed Runway XXR in ZZZ. I got up to cruise and I got a sinking feeling that I forgot something or I was missing something and I looked around to see what I could see. I thought and knew I saw the Master Caution Annunciator on the preflight but I second-guessed whether or not I saw it during my run-up. So I did what any curious pilot would do and tested it. I failed one generator to see if the warning light would work and it did not. Turned it back on and failed the other and it did not work again. So I checked the MEL; called dispatch on the radio; and turned back to ZZZ for the maintenance item. And on landing; I never got a Master Caution Light with reverse not ready and I did not get the light upon shut down. After it was shut down the light worked again. I tested the master caution light in flight to see if it would give me an annunciation and it did not. I believe vibrations on the airplane when it is flying. It works just fine on the ground. I asked dispatch over the radio what they wanted me to do along with check MEL to see if I could defer it in ZZZ1. I turned back to ZZZ and had maintenance look at it. I think it was just an intermittent failure.