I think I know the answer... see if you agree with me.
I was riding this morning down I-10, stopped at a rest area, and hopped back on. It looked like it was really dark on the road, and realized the headlight was out. I keep going, flicking it between low and high beam, again, no dice. I pulled over, turned the bike off, and back on, the head light was still out. I got to work, and on the drive home, saw the headlight was on. Checked it again this afternoon to see what it might be. I did check all of the lights, and had no issues with it.
I would imagine that there is a short in the line somewhere. I was wondering if anyone might have any ideas where to look, or any other things it might be.
-Nick
Old bulb maybe? It might work intermittently if the bulb is close to burning out. I had the same issue years ago with one of mine. Replaced it and it was fine - $20 for the bulb.
If it was a short you would have a blown fuse. Check your wiring, and switch before replacing the bulbs.
Maybe also think about a loose connector or poor ground, or possibly a sticky relay. Sometimes tapping on a relay can free it.
So, IIRC, the starter switch shuts off the headlights while the starter is engaging. With time that mechanism can get contaminated and the contacts get corroded. And then after the bike starts the lights don't come back on. But, in your case, later in the day the mechanism was warmer and the problem didn't recur.
I've used a deoxit spray to clean the shutoff switch and i think this would also work for that headlight contacts. Don't use WD-40.
Hopefully some more experienced mechanics can add more detail.
Mark