Hi,

The connector of the C-18389 "Sound Board" is quite simple: Indeed, pin 1 and 2 are unused.

When you hold the board, facing the components side with the big metalic regulator at bottom: the A7J1 connector is on your left (of course with the copper contacts on the opposite side). The pin 1 is at bottom (near the diode group), the pin 12 is at top (near the resistor group).

The connector with wires, coming from the CPU has the same numerotation. It's easy to identify pin 1 and 2 because they are not connected.

The only voltage to take care on the connector is the power: on pin 11/12 is the Ground. On pins 9 and 10 you should have the alternative voltage (about 12 VAC).

Pin 8 is the audio output.

All others pins are commands: there is no voltage here (pins 3 to 7). The drivers/cpu boards drive them to the ground when needed.
On the soundboard, there is pullup resistors to maintain a default voltage of 5v.

So, when rewiring the A7J1 the only things to take care is the AC power on pin 9 & 10, ground on pin 11 & 12, and the oudio output on pin 8.