Thank you for your answer, Elektrodrive.

Yes, the controller is as you said an alloyblock, and a plasticbox. What is the controller exactly doing? - I've got a wirediagram by email, and the circuit looks quite simple.
As far as I can se from the diagram, the coils are negative-triggered/fed with a positive constantly.

Btw. in the diagram, tractioncontrol is mentioned - Is this like in a car? Mine is spinning the wheels easily, so i guess this is broken.

What is the idea with 4 switches on the steering hub? 2 of them seems to activate a contator (Not the same as starts the hyd-pump), when the wheel is fully turned.