The switch is wired up so that when activated, it pulls the signal to LOW. There is also an LED on the board that will light up when the switch is activated. It uses a standard 4 pin 100″ pitch header and accepts a standard, old-style CD-ROM audio connector cable.
The mechanical endstop is a simple solution to a simple problem. We want to be able to detect when an X/Y/Z stage has reached its minimum or maximum. Instead of messing with flags or complicated light beam interruption, we use a mechanical switch.