I would guess you have burnt contacts in the LHS switch assy (quite common problem on the old K's).
To verify, disconnect the switch assy, the connector you find under the tank, LHS side, 8 pole.
Input is a white/yellow wire, output is a yellow wire (low beam), white wire (high beam).
Try to bridge the input and each of the outputs at the harness side, to see if it makes a difference.
Add headlight relays, to avoid this problem in the future..............search Eastern Beaver.