You just wire the relays to the control wires coming out of the wall. You can turn your furnace on and off by just touching these wires together. It will depe

You just wire the relays to the control wires coming out of the wall. You can turn your furnace on and off by just touching these wires together. It will depend on how your system is wired there can be a lot of variations. Of course making sure your product works with all those variations is one of the hard parts that they didn't address.