I have the pot in line before the amp using the signal from the + speaker wire inputting to the amp. Input is tab 1, output tab 2 and earth tab 3.
silly question but have you also connected the " - " speaker wire from the pin to the earth or " - " on the amp?
also do your experimenting with a cheap mp3 player, connect it to the amp first and get it working before hooking it up to the pinball, that way if you have made a mistake or there is a fault in your amp and it is throwing voltage out the input you won't go damaging your sound board on your pin.
what are you using for a power supply?
and as ajlaird said a schematic would help
