The Game I/O setup on the Apple IIGS is exactly the same as the Apple IIe:
the DB9 connector on the back of the machine and the 16 pin DIP socket on the
main mother board. The DB9 connector has four analog inputs, three button
inputs, power, and ground. The 16 pin DIP connector is the same but has a
strobe line and four single-bit outputs. For pinouts, see the IIe Technical
Reference Manual.