Air conditioner fan speed switch

If your switch works crisply, you might get away with cleaning and lubing it. I just used spray contact cleaner and Zep spray lube. I'm still using the original switch and keeping the NOS on the shelf.
To answer your question, my 1968 has a blower motor resistor. I'm thinking your '66 probably does too. If it turns out the switch isn't the issue, get ahold of the wiring schematic in the service manual for more info.