Chances are that this device is working, hence the clicking. What is not working is the cruise control amplifier, most likely mounted on the steering column not far from the floorboard. Do a search to see how it can be fixed by resoldering.

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Semibodacious Transmogrifications a Specialty

1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)

"Time flies like and arrow, yet fruit flies like a banana"
---Marx (Groucho)