The switch closure sends a signal back to the CPU which then triggers a score on the display. You really need a  schematic, but switch matrix is A1j7 pins 10 through to  17.
Switch is also diode protected so first call would be to make sure this works as if its gone open then no signal will go back to the CPU..

Sys1 diags can be found here..

http://www.pinrepair.com/sys1/#tools