Not sure about the "Fightstick" in particular, but this guide to
modifying Sega Genesis controllers for use with the Vectrex shows
with diagrams how to rewire the direction and fire buttons:
http://www.playvectrex.com/vectech/controller.txt
If the Fightstick has an analogue joystick, then you'll need to
wire it up differently with a circuit designed for the Fightstick
in particular.
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