Finally some nice weather so I decide to ride the 1983 R100RS down to St Louis to see my son. About an hour from home, the volt meter drops to just a hair under 12 and the red generator light starts to glow faintly. Normally the volt meter points to between 13 and 14 when cruising at highway speeds and, of cours, no red light. I need gas so I stop, fill the tank and have a short pit stop. When I restart the bike, volt meter goes back to between 13 and 14 and the red light goes out. Stays this way for the remainder of the trip (two more hours). The bike has 63,000 miles on it and had a new battery in April 2016. When not in use the bike is always on a Battery Tender. Pretty sure the bike is sending me a message here and since I want to take the bike on a trip this summer (1000 miles round trip) would appreciate hearing any ideas about what is going on.