My endstops have 4 female plugs, but the examples on the RepRap Prusa i3 Site have 3; what are each of them for? The Sainsmart Endstops I picked up are different from the ones described in the RepRap Prusa i3 Rework electronics assembly wiki;  they have 4 female plugs that go into the RAMPS 1.4 board instead of 3:



Since these endstops are different, how do I hook them up,  and what do the markings on them mean?
The website shows exactly what each wire is for.  Both middle wires are ground, the wire on the same side as the lever is the signal wire and the last wire is the power wire.