Help trouble shooting a cruise control servo - 95 F150

1995 F-150 I think I've isolated the crusie malfunction in the servo. All my lights work, no air bag light and no broke fuse that I can find. My cruise began to fail intermittently, and now it doesn't work at all. I'm inside the box at the end of the cable and I see nothing obviously wrong. Is there a way to trouble shoot this part? How can I tell if it is the problem for sure?

Norm