i guess a standard P5000 diagram might get you by for basic circuits but they did make quite a few changes in these trucks over the span since they were introduced. Plus there are 3 different wire harnesses for these trucks depending on which model and the options it had when it was made. Usually a standard wire diagram will cover most of it but....

with that being said you will probably want a more accurate diagram and having a FULL truck serial number will get you the exact diagram for that truck in most cases and there wont be as much guess work involved when checking and reconnecting circuits and identifying wire colors or numbers.