on the left side of the fuse box there are locations marked "ING" which means they have power with the key in on position. The power wire goes to the switch, the other side of the switch goes to the relay to trigger the relay when you turn the switch to on position. I'm not sure what you mean by the AC wire from Hayden.
I looked up the wiring diagram from the unit and that AC wire is an option which will bypass the sensor and turn the fan on as soon as the AC turns on..you don't need to connect that wire since you have no AC. The wiring by this diagram is pretty straight forward. I would follow the diagram and use a 3 position switch so the fan will go on at the temperature you set. If you don't have it to go on automatically you may forget to monitor your gauge and the engine will overheat.