http://userweb.windwireless.net/~jimc/vdocc1/vdocc1.txt

http://gdl-online.com/testproc.html
http://gdl-online.com/test021.html
http://gdl-online.com/test023.html
http://gdl-online.com/test024.html

The above links will give you all that you have been looking for to checkout, troubleshoot & repair all 14 pin MB/VDO Cruise Control Systems.
This includes the Amplifier, Actuator, Control Switch & Speed Sensor.

If you want the schematics...I will send you the pdf two page file. Email me .... sidoog@aol.com
Page two schematic shows a simple Speed Simulator to build with less than $20 of Radio Shack parts.
The I.C. chip for the simulator is Radio Shack #276-1718@$1.69 (This is an 8 pin 555 timer I.C.)
The 8 pin chip socket is #276-1995, $.69
The board to mount the socket...276-159,$2.4992-pack)
The pot is #271-002 (500k ohms),$3.99, instead if 150k but will work ok if you don't have a source for a 150 k ohm potentiometer.
33 ohm 1/2 watt resistor,$.99(5-pack)
10 ohm 1/2 watt resistor,$.9995-pack)
.1 capacitor, $1.49(2-pack)

I repaired a Cruise Control for a 1983 300SD with the above info. (all transistors & I.C's worked after a full circuit board re-solder)
I also bought a pack of alligator clip test leads & some momentary contact switches to connect to a 12vdc supply.This allowed all parts to be set-up on my workbench,operate & check out.
TIP...Before resoldering ALL points on the amplifier board I used some JASCO LIQUID PAIN/VARNISH REMOVER (Available at Ace Hardware)to brush onto the amplifier circuit board bottom. This removed the clear coating & gave me clean access to re-solder.