Ben, there's nothing special about installing it. Two screws, unclip the harness, now the old ones off. Clip the new harness on the new third into the truck's harness, put it into position, tighten the screws, done.
Now, I don't know your truck's year, but if you've got a 04+ and want the cargo lights to be functional, you'll have to do a little wiring. Very simple mod. Once you do it, the cargo's will turn on whenever your dome light is on(so it's whenever the door is opened which I think is super neato and I'm gonna do it to my truck).