[fyrffytr1]

I have an old 66 switch out in the shop I can look at but, I think there is a small set screw on the side of the knob that holds it to the shaft.

Edit:
I just looked at the switch and there is a small set screw that holds the knob on. Loosen the screw, pull the knob off then unscrew the bezel. Before you change out the switch try tightening the set screw. Sometimes they get loose and the knob may turn but the shaft doesn't. If the screw is loose you may have to turn it slightly while tightening to make sure it seats on the shaft properly. And, yes the switch does "click" when turned.