Switch edge test shows one microswitch (switch 35 here) as permanently closed even though nothing is pressing it.

Switch always reads closed but is not pressed: microswitch wired to the wrong lug

Cause: The switch had been rewired with the return wire on the wrong lug, so the circuit was made through the normally-closed side.

Checks

• Compare the wiring with another working microswitch in the game.
• Normal arrangement: the diode's banded end on the common (COM) lug, the other wire on the normally-open (NO) lug. The normally-closed lug is only a tie point where the strobe wire joins the diode's other end.
• Make sure the unused lug is not bent against its neighbour.

Fix

• Move the wire to the normally-open lug so the switch only closes when actuated.

Systems

• Williams System 11C

Games

• Whirlwind

Related tips

• A switch does not register in the switch test
• A whole switch row or column is dead
• How wiring faults show up in switch test
• One playfield switch does not register
• A whole switch row reads as the next row: fault in the row wire harness

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