I can see on a newer truck as wiring got more complicated and had some flex print and ignition changes, etc., and electric went to electronic, analog to digital, that harnesses would have to be more "custom fit" possibly...but on an old truck, it cant be simpler. Albeit grounding is a real problem with them and is the cause of trouble more than %50 of the time.
Using the body, frame, motor, sockets, brackets, bolts, screws and intimate contact for ground creates dozens of places to corrode, get loose, get isolated, rust out, break and cause intermittency and failure. Over and over again. I've never blamed a new harness for anything. It's just a bunch of wires, most of which come out of a fuse box. The correct hook-up is up to the user.
