I was having a furnace problem. I checking things out, I had 118 volts at a switch but not at the furnace. Probing further, I checked some other things and now I only have 79 volts at the same switch that I once had 118 volts? And still no power to my furnace. Any help would be appreciated. Thanks.

I'm going to have this thread moved to the Heating and Cooling forum. At this point I suspect it is more of a furnace issue than a pure electrical failure.

Just curious though, did you check the output of the circuit breaker to make sure that you didn't accidentally trip the breaker while you were trying to test things?

I agree with Don. Start at the breaker & trace until you get a voltage drop. Don't forget the emergency switch.

Is it a gas or electric furnace