Thank you. I'd rather not rig something up where the furnaces AC is literally connected to a two pronged ac to dc wallplug transformer like that one my humidifier uses. I think all I really need to do is put the relay between the power going to the humidifier motor. It seems like the simplest solution to me. I just don't want to drive that relay off the wrong wires, so I'm hoping do get that cleared up.
Thank you all the same
And yes you are exactly accurate:
what is want is so the humidifier comes on when the air is too dry AND the heat is selected.
I believe the setup should be, wall socket > wall ac to dc transformer > power wire from that to humidistat (old analog one) > line to relay switch > relay switch to humidifier motor.
Heat controls whether this relay switch is on or off. When heat is on, switch closes, circuit to humidifier is complete. When heat is of, relay switch opens, circuit to humidifier is incomplete.