Sounds to me as they found an open circuit on the dash harness. Probably between the column and the area where the wires interconnect through the firewall to the engine bay harness.

I wouldn't pull a dash for a fix like this. Just cut both ends and splice a wire in.

Next time it isn't working try the diagnostic method:
Do not start engine during this test. Transmission in Park or Neutral with parking brake applied.

Put the key in the ignition and hold the OFF button on the speed control then turn the key to the on position and then release the OFF button. This puts the speed control in diagnostic mode.

Within 5 seconds of releasing the OFF button, start pressing the buttons in the sequence shown below:
ON
RESUME
COAST
SET/ACCEL
(For each button pressed, the speed control light should flash ONCE, indicating that the pressed button is working.)

If, after pressing the last button (SET/ACCEL), the speed control light flashes:
2 flashes - defective brake pedal position sensor and/or a bad clutch pedal position sensor or the circuit is defective.
3 flashes - Brake deactivation switch is open or circuit is defective.
4 flashes - Vehicle speed signal is out of range or circuit is defective.
Immediately after the last flash code is complete, the speed control servo will pull the throttle open and then release it. This should be watched to check that the throttle and cable are not binding or inoperative for any other reason.

Although it is rare, it is also possible that this code could flash early during the diagnostic procedure.
5 flashes – Speed Control Actuator defective.
Turn ignition switch to the off position after test.

__________________
Automotive Electronics Engineer
2000 XLT 2.5L A/T
Mods:
Explorer OHC
Explorer Autodim Mirrors w/ Autolamps
Explorer Sport White Face Gauges