DH - the "off" function on RH control is for the engine not the HL. The rocker switch for HI/LOW is on LHASA control.
Yep, the dimmer is on the left control, but the on/off on the right control is for the headlight. My K0 550 is identical to the switch in the
pic, with as many wires and color coded the same. A K3 bike I believe will have a 5 wire switch on the right control with no on off, and be wired accordingly. I think the 550 changed in 76 model year along with the K6 750, and of course, they're different than F models. I'd guess the O.P. could use the brn/wht wire to power a headlight or a relay for one on his custom frame.