I have an older Janitrol forced-air furnace in my house. I have an old Honeywell programmable battery powered thermostat that has two wires going to it. Red and white. I want to hook up my Nest thermostat and know that it's best to have a common wire. I have tried it without the common and my Nest just short-cycles my furnace. I ran a new 7 wire (to future proof and potential add of A/C) from the thermostat to the furnace. Anyone have any idea where to add the common wire? In addition to this wiring, I have (but do not use) an air humidifier that is tapped into a water line. I have to look again, but in this Pic, you see the red wire tied to a black wire. I think this goes to the air humidifier so I can probably remove that. The other wire here besides the white is probably the red. Thanks.