I found this install manual. See if it is the right one for you.
I suggest disconnecting the brown wire from the harness (this is the door switch switch wire) and grounding it to the frame.
The step should close.
If it does the door switch is the issue. The door switch should short the brown wire to ground when the door is closed. It is suposed to be a normally open switch and it is not.
If shorting the brown wire to ground does not close the step then retract the steps and then disconnect the step 12 volt feed wires for five minutes. Close the door. Then apply the 12 volt power to the steps again. If you can locate the step power fuse you can do this by taking the fuse out when the steps are closed.
If this does not reset the step brain you have a bad step controller.
Let me know. I am curious.