You have to go around and activate all the switches, one-by-one, by hand, or any switch(es) you suspect not working. The display will show you if they're working or not, usually by displaying the switch number. If you find one or more that do not respond as working, the next step would be to check the wiring on any switches that do not respond in the test, and replace the switch if needed. Many times, a wire has just come off, and you'd have to solder it back on.