You need to wire the humidistat onto the humidifier accessory terminal on your furnace. one wire will be attached to the Common connection on the furnace and the other onto the connection on the furnace marked Hum for humidifier. I am assuming that you have these terminals on your furnace. Mine did. These connections are on the furnaces 24volt connections panel . It does not matter which wire goes to the Hum and which goes to Common, they are interchangeable. Hope this helps. By wiring into the furnaces blower circuit, the humidifier will only turn on when the furnaces blower is on.