If you go to Autozone.com (or one of those sites) I believe they have factory wiring diagrams.
IIRC there is a regulator box that has a wire that goes to a temp sensor on the manifold or slips into the radiator and one hot and one ground, they're pretty simple to wire up or at least that is how the aftermarket fan I used to have years ago was wired up. I'd put an inline fuse to avoid any shorts and make sure your temp gauge is working really good just incase the fan craps out on you. It can a gamble installing those, especially if they're used...