The lane change (flipper) switches and the ball shooter switch never register, though the switches themselves test fine.

Lane change and shooter lane switches don't register: failed column driver Q42

Cause: These switches share one matrix column, and that column's driver transistor Q42 on the CPU board had failed.

Checks

• Unplug the switch matrix connectors at the CPU and run the matrix test there with a jumper to see if the column works on the board.
• Check the column wire (green-violet) between switches in case of a break.

Fix

• Replace Q42 on the CPU board.

Systems

• Williams System 11A

Games

• Big Guns

Related tips

• Matrix burned by the lane-change switch touching the flipper EOS switch
• Inlane, outlane and drain switches all dead: blown switch transistor Q49
• Testing the switch columns with a clip lead
• Connector 1J8 switch column pins
• Switch matrix dead after an under-playfield adjustment with power on
• Row or column error: CPU board or playfield?
• Fixing a dead switch column on the CPU board
• A whole switch row or column is dead

Source: Pinball Repair help group!! (Facebook group)