cruise control 1994 Mercedes E320 convertible

[Quinten]

Hello cruise control wont turn on I checked the fuse its okay it worked then just stop wondering if I need to replace the cruise control module

[Rick76]

Do you have any idle problems, surging or stalling?
The cruise control module located under the passengers floor mat also controls the idle speed. The '94 suffered from disintegrating wiring harnesses and this includes the harness going into the throttle actuator.
The electronic module itself if quite reliable for that year but you could have a problem with the throttle actuator, stalk switch, or speed sensor in the instrument cluster. Do you have any brake lights out?
Did you check the fuses visually or with a meter?

[Kestas]

I'm working from memory, but I believe the brake switch, located above the brake pedal, can go flaky and affect cruise control. Also, if the trunk mounted brake light isn't working, this may affect cruise control.

If the engine wiring harness is still original, then I wouldn't start diagnosing any such problem until that is replaced. Same goes for the throttle body wiring.