Wiring for a trailer

1990 Cherokee Laredo. Can anyone give me a good description of how to wire a four way plug on for a trailer. I have looked for instructions on the net but cannot find any so I thought I would ask you guys. Also, a parts list and a good place to get them would be very helpful. I am putting the hitch on this weekend and would like to get it wired so I can pull my little utility trailer. Thank you.

Try this:
http://www.lunghd.com/Tech_Articles/Towing/Trailer_Wiring.htm