Test and Service Credit buttons are off the JAMMA harness. the Volume Up/Down buttons come off another header. I think it might actually be labeled "Coin Door", or "Aux. Inputs", I forget what it's called on the Seattle boards.
that should work, I have the carnevil kit and the service and test wires where cut off. so insead of wiring them up with the volume buttons, ill just use the service and test buttons in the cabinet.