Originally Posted by 14GuineaPig
OP says that when he removes the seat, the light comes on. Doesn't the wiring harness sit very close to the seat at the rear of the fuel tank. Just a guess but maybe a pinched/broken wire in that area that gets moved when the seat is in place. Try taking the seat off. Then try pushing/moving the harness to see if you can make the light go out. It should not be a short to ground otherwise it would blow the Lights fuse. I don't have the wiring diagram in front of me but many times HD uses a Orange/White Stripe wire to bring power to the lights.
You could also try checking for power at the headlight plug the next time the headlight fails before removing the seat.
That is where I would start but also remove the tank console. The problem may just jump right out at ya. Could even be a loose connector under the console.