A switch in a stack acts when a different switch closes, or a fuse blows when a stack operates.

Neighbouring switches in a stack short together

Cause: The gray fish paper insulator between switches is worn or torn, letting blades from adjacent switches touch.

Checks

• Inspect the fish paper in each stack.

Fix

• Replace damaged fish paper.

Systems

• Electro-mechanical

Related tips

• Tighten a switch stack before adjusting it
• Adjust a leaf switch at the stack
• Bend switch blades at the stack, not along the blade
• Gauge switch health by trying the stack screws
• A switch blade has lost its contact

Source: Repairing Electro-Mechanical (EM) Coin Operated Games to 1978, Part One, Clay Harrell (pinrepair.com)