Both my '85s suffered from the same problem ... occasionally it even starts to turn over but all of the sudden dies. Jiggling the wire worked 95% of the time and I'll be good for a couple weeks, then it happens again. The common denominator was they both had Autolite rebuilt starters in them. In one truck I have replaced the starter with a new NSA starter (not a rebuilt) and so far no problems (about a month now). The other truck is awaiting its transplant.

85 XtraCab SR5 4x4
85 XtraCab Deluxe 4x4