Is there a wiring diagram for a 1985 full size Chevrolet Truck?

You can go to the AutoZone website and enter your vehicle. They have online manuals and wiring diagrams available for free.

yes have both engine and chassis wiring in my workshop manual , can be reached at egood7@live.jp

haynes repair manual or chilton repair manual, most often found at your local parts store

That year did not have one on it.

try the back of a chilton or haynes manual