Welcome Steve!
You probably want to start with the Electrical and Vacuum Troubleshooting Manual:
https://www.garysgaragemahal.com/1986-evtm.htmlWhat specifically is the trucks problem?
Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.