From the sound of things you may have an aftermarket switch. I have a ' 72 Super and the stock switch is a lever which protrudes from the right side of the steering column. One position up is low and the next position up is high. Both operate at a fairly leisurely speed! The lever is part of an assembly which is attached to a larger assembly which is your turn signals and high-low beam for the headlights. The whole shebang is prone to collecting dirt and dust ( and in the case of MY72BUG grit from sandblasting) and can pose problems for the restorer. On the plus side the assemblies can be removed by removing the steering wheel and a few attaching screws. New ones are available but a good cleaning with electronic circuit cleaner and a blast of compressed air will likely fix it as long as the wiring and motor are good. If your unit is not this stock one the "knob" could go on in a number of ways. If your unit is a stock one and you have a lever rather than a knob you will have to remove the assembly and see how it was attached at the factory. Removal is not very difficult. Good luck with the work. Dan (MY72BUG) in Goderich
I'd rather have a partial bottle in front of me than a partial frontal lobotomy.