https://groups.google.com/forum/#!topic/deltabot/k10ernLi7LU
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If you're wiring your endstops into the X3's min connectors, the nice locking ones, you'll need to change the pin assignments in pins.h. I forget what the min pin assignments are but if you search in the groups there's a message which says which the right ones are. You'd probably be better off wiring into the header pins behind the min pins. That way you won't have to remember to change pins.h everytime you grab a new copy of marlin.
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I used the low pins, so I didn't have to move the screw terminals, but I'm using repetier and I had to swap the pin numbers in pins.h
#define X_MIN_PIN 3 = now is -1 to disable
#define X_MAX_PIN 2 = now is 3 to enable on the low pins on the board