Wayner, This real simple.
Connect the Blue wire from the Slugbuster to terminal #4 (Coin Switch) on the GS-9. Connect the Yellow wire from the Slugbuster to terminal #5 (24Volt Hot) on the GS-9. Connect the Black wire from the Slugbuster to terminal #7 (Common) on the GS-9. The Purple wire isn't used unless you've got a coin counter connceted. This should do it.