Yeah, its neutral safety switch most likely..
Um, lets see..
Wiring diagrams aren't the greatest. I had this issue as well. My truck is an 1983 frame, with a 1985 cab from an automatic with a 1985 22RE from a manual.. lol, great stuff. Well, first I ran the 83 22R..
Here's what you are looking for:
Over on the engine harness in the engine bay. Somewhere on the right side of the engine bay on the harness, there's a large-ish round connector that would have gone down to the transmission, so its probably not connected now. It has 3 wires, two are big and black, about 12 gage or so. The other is smaller.
The two big black wires need to be shorted together, in the harness. I cut them at the connector and soldered them together. I believe given the wire size, that it carries a bit of current, so make sure its done good.
That *should* solve the problem, if not, let me know, I'll take pics. I have the online 1985 service manual, you can also go to autozone.com and find the wiring diagrams (I posted a thread on them in this forum somewhere) they are scans from a chiltons manual, may or may not be helpful.
Good luck

We'll get 'er going...