Mercedes Benz W126 560SEL 3/89 Testing & Overhaul of Electrical System and All Control Units Part 10 

Conclusion of the Cruise Control Issue:
The clutch control circuit is toast in both control units I got
One with replaced capacitors one without.
I had a second actuator unit which I soldered into the control unit to make this video
The Speed signal on this Speedometer is a Square wave starting at 30MpH with a 75 Hz
8 to 12V 20% duty cycle square wave
So since it is linear 60 MpH would be 150Hz
The options are:
1. Buy a new / refurbished unit
2. Sent these two I got in for repair
3. Last but not least, fix it myself which I won’t do because I don’t have the schematic and I don’t feel like getting into this circuit on this involved level