The Dodge cruise control only operates after 30mph. If the Cruise Control Light light comes on when you press set and goes off when you press cancel or put your foot on the brake the computer is seeing power and brake light switch and the input from the cruise control master switch. The actuator that opens the throttle in the engine compartment has a dump valve that is grounded by the computer to dump vacuum to not allow the actuator to apply throttle when you cancel the cruise control. Brake light switch should have power at yellow/red wire, brake light switch at rest power should travel through brake switch to actuator in engine compartment to the dark blue/red wire. Black wire at actuator is ground, the vent solenoid and vacuum solenoid get power from the dark blue/red wire internally in the actuator, tan/red wire gets grounded by computer to operate the vacuum solenoid and the light green/red wire gets grounded by the computer to operate the vent solenoid. I suspect a problem up at the actuator but need to test it.