The LEDS operates with so little current that even a drop of water across the ON-OFF switch may pass enough current to make them come on... That has happened to me as well on one of my ceiling LED BOARDs I installed in my trailer. I actually had a pin hole through the roof right above my light fixture and I repaired it with a screw and sealeant screwed into the small hole. It was not a good seal... Then everytime we had a real long rain this would happen to me as well...
Made me fix my small hole better haha...
Perhaps you can spray something all around where the water may be coming into contact with the on-off switch or cover it with electric tape or heat shrink etc...
Roy Ken
