Strobes are shared between the switches and lamps in Sys3 games. What this means is that if you have a problem with the lamp matrix (short/bad wiring/bad diode/bad LED), switches will not work properly during the game.

The problem is that in test mode, the lamp matrix is not active so it is possible that all switches test out properly in switch test but then don't function properly in game play.

To diagnose this issue, you must run the individual lamp test and check for any sort of ghosting in lamps other than the one in test. If you have it, you have to chase down the lamp problem and correct it. If you don't you will have problems with switches registering in game.

This subject has been written about countless times in the forum:

https://www.google.com/webhp#q=gottlieb+system+3+switch+matrix+problem+site:pinside.com

Search is your friend.

viperrwk