Just because you have the switches does not necessarily mean that the heaters are installed. In my Vegas, I had them. In my Axis I do not, but I still have the two switches. Look under the black tank on the driver's side and see if the heating pads and wires are attached. If you do have them, I do not believe that there is a minimum amount if water that needs to be in them, but I would make sure that there was some water in them before I turned them on.
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