Take your time and have a second person help you. Install is fairly strait forward. I did have to remove the inside headliner to install my speakers, (Pioneer brand), but that wasn't too bad. The cab top has to come off too, just be MIGHTY careful not to damage the cab seals. Wire harness is there, but you need the harness to mate up to the JD plug. It is the same plug as from a 1986 and up VW car. Or the JD kit should have it too. I just did aftermarket stuff as it cost me under $150 for radio, speakers, wire, etc. and my free time.
Oh... and this was on my 3720. Do a search here as thats how I learned how to do my install, and other important info too. Glad to help you if I can!!