Stick your ear next to the front brake handle. Squeeze the handle and see if you hear it clicking. My '99 had issues like that. Maybe it would work, maybe it wouldn't. If you don't hear it click then the plunger switch is not fully activating the light.
I was preparing to replace the switch and started to tear into it to see if I could fix it or replace something. I found the microswitch. I sprayed some contact cleaner and soaked it real well. Exercised it well, stuck it back in the bike and haven't had an issue in over a year.
1999 BMW 1100GS
2012 Kawasaki Concours