I was wondering what test equipment you use on EM machines for trouble-shooting that you find invaluable and also what items you would love to have if they existed. As a new owner of a 1977 Williams game, trouble-shooting relays, cams, switches and such by myself is tedious at best. One thing I would love to have is a plug in buzzer that you use in place of a 6.3 V lamp that would make a noise if a switch is made, or a buzzer that connects across a coil that would beep if energized even for a moment. Any thoughts? Do these exist now? I have a 3D printer and have started thinking that making some EM testing tools might be fun.