Cruise control not shutting down

I have a friend who has a 1998 Chevy Lumina and his cruise would not dissengage. It also made the car go faster instead of slowing down. He tried braking, switching it off, but it wouldn't work, he had to use his brakes and emergency brake to stop his car. What would cause that to happen? It is currently unhooked. He would like to hook it back up, but is afraid to and fears the cost of getting it checked may be real high for maybe a small problem.

I agree, the tail light switch mounted on the top of the brake pedal is the trigger to shut the cruise down. The way that the switch works is: the light switch is depressed all of the time while the brake pedal is at rest. When you push the pedal, the switch makes contact which in turn sends a signal to the cruise to disengage. If the switch is stuck, your cruise will not disengage and your brake lights will not work. There is a cable connected to the throttle linkage on the throttle plate, if that sticks your jammed up too. The part that worries me is the fact that he couldn't power it down to disengage it. That makes me think that it's not the switch and maybe a module. The speeding up thing is probably just that fact that the cruise is still active and he's trying to stop. The cruise will try and compensate by speeding up the engine.HotRod

Thank everyone who posted a comment on this. I am going to take a look at his brake switch and all cables. No, he doesn't have any special lights in his car.