If there isn't an existing harness under the seat, you'll need to get one. On my 2004 (with power/heated seats) there is a multi-pin harness (10 wires in all) that comes through the carpet and plugs into the seat wiring. That being said, I don't think you'd be able to wire a single 12vDC power feed to the seat switch. However, I could wrong. Like Boondocker said, when you buy the seat (like from a junkyard), make sure you get the entire wire harness along with it. Usually you can get junkyards to throw that kind of stuff in with the sale for free. Good luck. If you really want to do it right, refer to a shop manual that specifically covers your year truck and wire it the way the the factory does. This will save you a lot of potential problems and aggrevation.
Ryan