i would think loose connection too, or at worse a short. check from the switch forward, it could be corroded causing a short.

 

I had a Fat Boy 10 years ago an the same thing happened to me at night . talking about shock ! I flipped the high beam on an there was light . phraise the Lord ! when I got home sure enough the wires where it goes thru the chrome head light bucket had wore a hole thru an shorted out . a little tape an I was rolling again on low beam . I hope I helped . Duane 08 Blue Ultra # 617849 Born 8-02-07

 

man, that vibration can really give us headaches.