While riding yesterday, I was on a slight down slope and was able to have the bike in 6th gear and in cruise. I tried to pull in on the clutch to see what happens with the 6th gear light. I know someone here said that the light went out when the rpms went up from pulling in on the clutch. I was able to pull in on the clutch "just" enough to turn off the light without disengaging the clutch at all; so rpms remained the same and the light went out. If you're putting it into 6th gear the light doesn't come on until you have the clutch all the way out, then it lights up.
I looked in the electrical drawing and found a clutch switch, but did not find a 6th gear switch shown anywhere. So I'm still not sure of what activates it other than what someone suggested; certain mph and certain rpm and ECM knows the gear selection and turns on the 6th gear light.
When I go in for my service and campaigns, I'll ask how it all works, if they know that is.