Might be the water pump switch for the fresh tank. That's where ours was located in our popup... Took forever to figure out what it did since we most always were hooked up to city water and never towed with water in the tank due to weight considerations.
If you haven't already located that switch somewhere else in the popup, I'd bet that is what it is for.
Make sure you have charged batteries or are hooked up to power and then put some water in the tank and turn on the switch and see if you hear it running. (humming sound) and get water...
2012 Flagstaff V-lite 30 WTBS
2011 Ford Expedition
4 kids and a hubby & never enough time to camp!
2011: 17 nights 2012: 26 nights 2013: 46 2014: 20 2015: 16