Do you have a test light. Does power go into the headlight switch and come back out?? Check the hi/low beam switch. I've had a headlight switch work on the marker lights but not headlights (Ford Truck) and on my old Honda if you went from high beam back down to low beam to quickly the lights would go out, you'd have to go back to high beam then slowly pull the stalk and gently release it...........switch was starting to come apart................if you don't find a quick fix then start at the start of the circuit and follow the power along to you find where the problem is.

Tom