Wiring harness is already on your truck. If you get the dealer part it should just be plug and play.
So I got under there...there aren't any wires going to the 'blank' holes for the fogs, BUT there is a wire and connector that is coming off the back of the rectangle lights that are in my bumper....is that what you are talking about? That would plug into the fog lights?
Then I would just need to find where that is actually running to.