An Ohm meter will get the switch functions sorted. B for power sounds right and the switch is going to make a circuit from b to one post or the other when turned to the first position. The ground is through the lights. Sounds like the heater control switch in my truck. But without the resistors. Light in the knob and it looks great at night on hi. Slow speed is pretty dim and both are not visible during the day time. So use the two you need and ignore the third post it won't be used. You might need to ground the light in the knob, maybe. It might just be in the circuit when the fog lights are on. Any way an Ohm meter will help figure what post is what.

Steve H