[Jared Russell]

The 15 pin connector that goes to a joystick - each pin corresponds to a particular function in the program. The document linked to earlier has the pinout description of what each does. To use a digital switch, for example, connect one terminal of the switch to ground and the other to one of the pins that corresponds to, say, p1_sw_trig (assuming your switchbox is plugged into port 1).

Then, in the program, whenever you access p1_sw_trig, you are actually getting the value of your switch.