The C6 can be a pain in the kiester, can't it.
I'm waiting for my 3rd from arturo to go into the new console.
I think it will be safe this time from shorting out since I ordered a 12v power supply just for it.
Your voltage readings are opposite what I got when I first tested it
but I am running a replacement circuit board not the original.
Still, I had the meter connected to the outputs of the C6 board not the pot.
I know the pot does work backwards, when you click it on(clockwise) it cuts power and when you cycle it all the way off(counter clockwise) it turns power back on.
I can't find the page on that but believe it has to do with the circuitry on the original board that prevents the motor coming on unless the switch is cycled off first.
Don't remember if it was from arturo or uncle rabid.