I believe that the slide has two circuits. One goes from the buss under the trailer at the tongue (the one you checked) and the other is fused in the main panel. This is the controller circuit that sends power to the in/out switch.
Wright and Penny
2010 Tundra 4X4 5.7L V8
2014 Rockwood 2604WS
Life is a cruel teacher. She gives the test first; the lesson then follows.