Check the voltage from the input side of the switch to ground. If there is no voltage, the problem is in the supply to the switch. Then, if there is voltage at the input side, use your meter to measure the voltage at the output side (to ground). If no voltage at either position of the switch, it's the switch.
2004 Tiffin Allegro 27.5 ft. P32 18,000 lb GVW. 8.1 liter. Workhorse chassis built May 2002. 24,500 miles. 2012 Jeep Liberty Toad. RVi2 brake unit.