I have an old Rheem gas furnace which doesn't power on. I opened up the unit and found what looks like a wire that has been disconnected. Can anyone tell me where this should be plugged back in (if at all?)

Pic of what I'm talking about

The disconnected wire is red and below where everything else is connected.

I tested the socket and it is powered. Turning the thermostat on fan does nothing.

Thanks!

Typically you can take the wire and it should be in the radius of the length of the wire.inside you unit there should be a schematic. On the wire there is a number a letters. Find that on the schematic and there you go. You might also look for wire that are piggy backed.