You forgot to connect “Add to Viewport” with “Bind Event to secondwidget_button” in Level Blueprint 
I’ve just got idea that you can do the light switching in other way. You can create a variable in the Game Mode that will hold an instance of the light switch. In Level Blueprint you can Set it into the instance of the light switch in the Game Mode. After that you should have access to the light switch from the Game Mode, which should be accessible from the Widget (Get Game Mode).