For clarification, the switch you're talking about controls the heating pads on the water/waste tanks in the camper and on mine, the switch is lit when on as are the water pump and WH (gas) switches. As you've had the panel off, have you checked for 12V DC to the switch itself. If you have 12V to the switch but none out regardless of switch position, the switch is bad and will have to be replaced.
If you need a replacement, it can be ordered through Rockwood parts dept.
Nights camped in 2013 - 55, 2014 - 105, 2015 - 63