Hi albertsneijMD. Welcome to the forum. It could be a wire rubbed through and shorting to the body or some other piece of metal, but more than likely it is just the speed control servo unit that has a break in one of the solenoids. The Engine Computer will disable the cruise control system because the affected solenoid could be the "Dump" valve which kicks it off when you press the brake pedal. It's a safety thing that's programmed in.
To find the servo, (I can't remember where it is on your vehicle), follow the two throttle cables back from the throttle body on the engine. One will go to the firewall to the gas pedal. "That ain't it". Follow the other cable to the servo. The servo will have a four-wire plug.
I autopsied a servo that I replaced under warranty and found a corroded spot where the wire had come loose. Resoldered it and it worked fine. In the 15 years since, I've only run into one malfunctioning servo. My reason for mentioning this is to show how little problems they normally cause. For that reason, I would have no worries about sending you to a salvage yard for a used one. If your vehicle uses the newer small black servo that does not use a speedometer cable, it should be the same part that is used on all Chrysler vehicles throughout the 1990s.
Before you go looking for a replacement, check the electrical connector for signs of corrosion. You can also perform resistance measurements to verify there is a problem in the servo itself. If I can dig up a service manual, I can tell you which pins to measure. If the servo test ok, you can perform the same measurements at the Engine Computer's connector. That will test the wiring AND the servo at the same time.
Monday, May 24th, 2010 AT 3:41 PM