its a bit more complicated on our trucks because of the PATS system on our trucks. www.the12volt.com will give you the info on finding your correct wires under the dash (usually pretty accurate). Then its just about matching them up with the corresponding wires on the unit itself.
I put one on my 98. The manufacturer should have a tech support page with the information you need. Mine was made by DEI. I used a PATS bypass kit bought on Ebay for about $5. But it is a lot of work to install it the right way. Good luck.