This stuff is from 1981 but I think the stuff you're looking at is the same and will help you (I don't remember what year truck you're working on (*hint* *hint* ))








Yes, getting a copy of the factory wiring diagrams will help you a LOT, they're pretty cheap on eBay and places that sell used factory shop manuals.

Even an EVTM is helpful in its own way, and is usually lots easier to read (but lacks a lot of detail).