I realize this is kinda old, but have you checked the set switch. I dunno if the trucks are the same as my LHS was, but the on/off:cancel button was screwed to the left side of the steering wheel and the set/coast:resume was screwed to the right side of the wheel. Or is it like brand F's where they're mounted in the wheel? Then I have no suggestion.
My cruise light came on also, but I would press set, nothing. Press set again, nothing. Do it again, nothing. &#$%!!! And I'm one lazy SOB, I wanted the cruise for the 3 mile road.
It turned out that my vacuum lines were fine, but the connections on the set/coast:resume button were either dirty, or loose. I unscrewed the button, took off the connector, turned it over and looked at it like an idjit. I shoulda took a picture, it would've been priceless. Well I was like whatever, I'll hook it back up, I don't carry spare cruise buttons around. Turns out it was just dirty or loose, it worked fine from then on out, until the car was totaled anyway.
Good luck,
this is so late.
Have a good one!!
Dan