loose wire? Short in the wire? Dirty or faulty hand control?

I'd start by messing with the low beam/high beam switch. Flick it back and forth multiple times, wiggle it around to see if your lights flicker. Could just be dirty. Could also be broken, probably a way to jump it or bypass it and find out but I couldn't tell you specifically how. I'm not a mechanic exactly, just lending my thoughts on what I'd do if it were me.

Good luck!