if you scroll down there is a photo that shows where people usually tie into the factory harness for key on power. they actually make an adapter for it so you dont even have to splice wires, but im not sure what that is offhand.
basically, the wire you are looking for is under the front dash... near the key. i think it is the wire that goes to the 12v socket on the fender.
Here's a link 5KM-86171-00-00 WIRE, LEAD 1
Cost is around $11. Connectors mate up to OEM connectors so it is plug in and use. Gives you 2 separate outputs for key switched power. I use one myself and like how it simplifies wiring for LED lights and winch. Best to use with a relay.