Extruder Motor does not obey comands

[chkthat]

Hi Folks,

For Christmas I got my I3 Pro B and finally i found some free time for this project.

I have solved the (seemingly quite common) problem with the z-axis motors on my own -> Potentiometers are all between 0.8 and 1.005V
I also downloaded the newest Marlin-Firmware.
I checked the wires of the Extruder with my multimeter. They are conductive and not broken.
The Thermristor works, (stupid as I am) I checked by touching it.
The Temp Sensor also works.
I swaped the motor drivers, they are not the problem.
Funny enough i swaped the y-axis Plug on the Board with the Extruder Plug and none of the motors worked.
Also I did heat up the Nozzle each time before testing whether or not my attempt to fix the bug worked.

I demontaged the Extruder-Unit to make sure I can see if the motorshaft turns.

Do you have any advice for me? I´d really like to start printing, i even got myself an arduino uno and some hobby servos. I intend to build a robotic spider :)