What determines the home position?

When homing the printer hits the end stops to calibrate. What is it using to sense the end or home position?..is there some sensor? or a load on the motor?

 

I dont get it as at all

I am having trouble to set the end 3mm screw to adjust it from repeatedly hitting the end.

 

 

There's a microswitch in each axis to tell the printer where the end is. You can hear a soft "click" during the initialization when each switch is hit.

I canot see any cable attachments for microswitches unless they are somhow attached to the grounding wire on the steppers?  

For the Z and Y (bed) axes the cables run through the inside of the aluminum extrusion since the microswitches don't move. For the X (crossbar) axis, there's an extra pair of wires bundled in with the stepper motor cable.

The MK-II has no microswitches, but uses motor load. One of the elegant features of this printer.