This cable connects 2 parts on the Extruder Controller to the 6-pin IDC connector on the Stepper Driver.
Quadrature (10-pin IDC) connections:
Pin 7 => Stepper Driver pin 3 (STEP)
Pin 8 => Stepper Driver pin 4 (DIR)
D10 (3-pin servo header) connections:
Signal Pin (green wire): Stepper Driver pin 5 (ENABLE)
Ground Pin (black wire): Stepper Driver pins 1 and 2 (GND)
Stepper Driver pin 6 (RESET) is not connected.
More info: wiki.makerbot.com/stepstruder-mk6-with-gen3