Holding Tank Heater Switch doesn't light up

[mambojambo]

My holding tank heater switch is not lighting up when I turn it on. Is this an AC circuit? There doesn't seem to be a ckt breaker for it. Does anybody know how to test the switch? It has three wires going to it which is confusing because if it is a DC circuit it would have two. There is a Black, Red, and White. White must be ground because it is going to brass. Winter is coming and I need to figure out if the switch need replacing or something else.

Forest River Sierra 323FK
Solomon's Rec Center
Solomon's, MD

[yvesm]

Its a 12 volt circuit. Its a 3 wire probably to light up the switch when its on. Mine was not coming on in my camper but after turning the switch on and off several times the heaters came on and the the switch light up. There might be a relay for the tank heaters to take the load off the switch but I am not sure. My 2011 Rockwood has heated tanks but the dump valves are exposed and not heated (go figure!!) I used a heat tape this fall to keep the valves from freezing. Maybe next next year I will install valve heaters UltraHeat - UltraHeat Webstore

Good luck.