After you pull the two plugs in the back that hold up the headliner (and cut the hole) the wiring runs from the rear dome light bracket welded to the roof (natch, but be careful that the wires go through and not around the bracket (you'll see it)), up the left or right side (it's way easier if you have the sunroof, because you can just pull away the plastic molding around the sunroof opening and reach inside to pull the wiring through), to the dome light at the front (you pull that down using a small screwdriver as a lever), and then connect the wires. I used the harness, but it really isn't necessary. It's much easier than it sounds, although if you don't have a sunroof you have to snake the wires a bit.
