You should call Heartland Customer Service at 877-262-8032 / 574-262-8030. Have your VIN # ready. They can tell you IF your coach was ordered with the YETI package (sometimes called the Canadian Arctic Package). It includes heating pads on the holding tanks, heat tape on the portion of the fresh tank feed line to the pump that's in the underbelly, and radiant insulation in the front and rear caps.
Switches and switch locations vary. Typically, the tank heaters are operated with a large, wall-type light switch that is illuminated when ON. The electric side of the water heater may have the same type of switch. There may be a separate smaller rocker switch to turn on the heat tape for the fresh water feed line.
You might want to take a look at our owner-written
Water Systems Winter Usage Guide for help on how to keep the water running in sub-freezing weather.
One point of confusion on RVs is the industry use of terms like "Four Season" or "Comfort Tested to Zero Degrees". Four season is relative, depending on where you live. Four season is one thing in Florida; quite another in North Dakota. Comfort Tested means that the interior can be kept at a comfortable temperature. It has nothing to do with the water systems.
We've taken 5 extended ski trips to Breckenridge, CO with temps as low as -30 (F). We're not the only ones there and I can assure you that every travel trailer, 5th wheel, and motor coach needs modifications and special treatment to keep the water running in that climate.