Mike, I'm guessing you're right about the water heater. I pulled the switch and found that the wires to it are heavy gauge, like #14 solid copper home electric "romex" wiring, so I'm guessing it's the electric heat cutoff switch, just find it odd that it's not labled. In the bathroom there are two switches. One is a small 12v
switch with red indicator light that I think feeds the 12v
circuit to the water heater for LP use. The other is a typical home-type light switch labeled "water heater" for the 110v element.
The coach battery disconnect switch just inside the front entry door activates-deactivates a relay in the rear basement battery compartment turning off all 12v
feed to the coach.
Thanks for your input.