I have a 1980 no AC. It has the factory 4 or 5 settings in a rectangle switch, meant to go on the original unit. My lines that control the blend doors are rusted in defrost mode and it broke my sliding unit. So I want to put a piece of PVC plastic and drill 2 holes in it. 1 for an on-off switch for the heat (its stuck on) and one for the fan control. Its a lot easier to drill a circle and use a switch from a store than to try to fit the factory fan speed switch in. Can I use one of those dial switched(much like the dimmer for the headlights) to control the fan speed? Because an on-off switch I already have, but keeping the fan speed control where I want it will be difficult.