The line leading to my FPR does not have any vacuum when I unplug it. Are the solenoids on the passenger side fenderwell near the firewall responsible for supplying vacuum to that line? If so mine might be bad. What exactly are those solenoids down there called?
Here’s a little better view of a vacuum diagram like the one Bill posted: 86-88 use the same vacuum routing.
Diagram courtesy of Tmoss & Stang&2birds
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.