A switch that tests good with a meter never shows in switch test, and the feature it controls (a lane change, a trough count) doesn't work.

Gottlieb System 80: a switch never registers: check its 1N270 on the diode board

Cause: On these games many switch diodes sit on separate diode boards, not on the switches. A failed 1N270 there kills that switch.

Checks

• Find the switch on the diode board using the manual's switch chart.
• Test the diode on the diode board, out of circuit if the in-circuit reading is unclear.

Fix

• Replace the failed 1N270 diode on the diode board.

Systems

• Gottlieb System 80
• Gottlieb System 80A
• Gottlieb System 80B

Related tips

• System 80 switch matrix diodes
• One or more playfield switches do nothing
• Lane change from the flipper button does nothing: bad 1N270 diode
• All tilt switches show as switch 26
• The three tilt switches on a System 80 game
• How Gottlieb switch blade numbers are laid out
• System 80 switch column 7 (coin door and tilt)
• Switch test (step 18) shows switches closed

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