On my '02, it's on the front panel of the kitchen sink, alongside one that switches ac power to either the microwave or the electric heater in the hot water tank.
If your set-up is like mine, you'll find it only heats the black and grey tanks (NOT the potable water tank) and the elements draw a lot of current from the 12V dc side of the rig's power system. The thermostats aren't adjustable and they come on at 40F, going off when the tank gets to 65F, according to the manufacturer's documentation.
My opinion is that heating the black tank contents to 65 degrees isn't that good an idea, and there's no logic in the system to prevent the heaters coming on when the tanks are empty. Pumping 80 watts into a 3" x 8" heater stuck to a empty plastic tank doesn't seem like a good idea either.
Georgetown spells "Arctic" with only one "c". To a Brit like me an "artic" is an 18-wheeler (short for "articulated lorry").
I don't plan on using the system at all, since we don't camp in freezing weather and keep the tanks empty when the rig is stored. The original owner specified it.
Frank and Eileen
No longer RVers or FR owners