I am having a weird problem with my headlamp on my 1983 Honda FT500. When I go out to start it in the morning, insert my key and turn it (engine still not started tho), the headlamp comes on as one would expect, and is quite bright. When I start the motor, however, the headlamp immediately dies. I think I have noticed that if I let the bike run for several minutes that the headlamp will come on again.
Update: Unfortunately I do not think it is a problem with the battery. Today I started the bike and let it idle for about 20 minutes. The light still didn't come on. Then I drove it around (locally only) for about 20 minutes. The light did not come on. When I got home I took the battery out and used a multimeter to test the voltage and it showed 12.85, which I understand to be quite strong. The bike starts quickly, too. So the fact that the bike starts quickly, and the battery maintains a strong charge even after a 40 minute idle + a 20 minute ride makes me think it is staying charged as well.
What would be causing this?