Lights in swimming pool not working
If you get power across the 2 terminals when the switch is &quot;on&quot; (closed), it means your switch has failed and needs to be replaced. Of course be sure to turn off the power before replacing and if this is a switch outdoors, be sure to get a high quality replacement and appropriate coverings for the code in your area.
EDIT--additional info: To test, with the power off you could disconnect the switch, wire nut the 2 wires together, turn the power back on and see if your pool lights work then.  Have you checked to see if they are simply burned out?