A switch closing makes an unrelated event happen, such as an inlane firing a slingshot or a ramp shot causing slam tilt.

Phantom switch closures: one switch triggers something unrelated

Cause: A shorted or miswired switch: contacts bent together by an airborne ball, a row or column wire fitted to the other end of the diode after a repair, a bad switch diode, or factory-miswired replacement ramps or kickers.

Checks

• With the glass off, start a game and close switches by hand to find the one that triggers the phantom event.
• Note its row and column, then the other three switches forming the square: for switch 53 those are 35, 33 and 55. The fault is very likely one of these four.

Fix

• Fix the bent contacts or correct the wiring, or replace the diode.
• Check the switch wiring on any new replacement assembly before installing it.

Systems

• WPC Alpha-Numeric
• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95

Related tips

• Two or more unrelated switches trigger together
• Slam tilt every game and random switch hits: bent switch diode
• Phantom switch closure that survives a new CPU board: bad 4N25 on the driver board
• Slam tilt when both slingshots fire together: sling switch wired wrong
• One switch also triggers another: corroded switch connector on the CPU board
• Random coil firing or slam tilt from weak 12 V (notably Theatre of Magic)
• A dedicated (direct) switch does not work
• WPC: phantom switch closures traced to a 4N25 on the -1 driver board

Source: Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part Two, Clay Harrell (pinrepair.com)