cruise ctl works intermitently on 2006 Ford E-250

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Cruise ctl works sometimes. other times just doesn't activate. What's up with the "sometimes" ???
(2) Answers
The cruise control system will not power up if the processor sees a fault with a component that is required to turn the system off as a safety measure (like the brake light switch or speed control cut off switch). Check those components -- do you have brake lights all the time?
Check all electrical connections in system. I don't believe this has a vacuum servo or would have you check for leaks.