I have a 3.1 91 GP and since I bought it the cruise control didn't work at all. I don't know much about cruise controls except the basics, anyway,  the fuse is ok and I checked the two vacum lines on the actuator the "thiner" line has vacum but the "thicker" one has none I don't know if it's supposed to have vacum from the line or from the actuator or none, I tried to follow the thicker line to check for leaks but it gets lost in the harness and I don't want to rip it apart until I know this is the problem.

  I hope some of you guys know about this.

thanks.

jalatorr@hotmail.com

Under the dash right behind the brake pedal is a vacuum switch that cancels the cc when you push the brake. Make sure that this switch is still in place. When you are not stepping on the brake that switch should be pushed in and then the cc system will have vacuum.