First question: Is your gamepad an active-low or active-high device?
Most encoders are active-low (connect ground to the input to trigger the output), but the ZD encoders are active-high. (connect 5v to the input to trigger the output)
Measure the voltage on a daisy-chained trace (common to more than one button) -- ground = active-low, 5v = active-high
If your gamepad is an active-high device, check out
this thread.
If your gamepad is an active-low device, wire it up like this with 12v to the recognizer and coin signal/ground connected to your gamepad.

The reverse-biased zener diode is there to regulate the 12v from the coin recognizer down to 5v -- use a zener diode rated for the voltage that your gamepad uses.
You may need to adjust the sensitivity or program the recognizer depending on the model you are using.

Scott