I'm trying to install a new Honeywell WiFi 9000 thermostat which requires a common wire. When I removed my old thermostat, I can see there are two extra wires in my wall (black and orange wire) that are wrapped around the bundle of wires. Can I use one of those as my c-wire?
However, when I go to my First Co. air handler, I can see that the black and orange wires are not connected to anything. The air handler wiring diagram says the brown wire is common. Could I just connect that black or orange wire to the relay terminal where the brown wire is connected to?