There isn't any specific location for the heater switch! According to the September issue of the 1931 Chevrolet Service News the fan motor switch and resistance unit can be installed in any convenient location on the instrument panel. A 33/64" diameter hole is drilled in the instrument panel for the fan motor switch and the resistance unit.
If you don't have the 1931 or 1932 issues of the Chevrolet Service News, you can purchase them from the Filling Station in Lebanon, Oregon. The Chevrolet Service News contains a lot of information regarding the hot water heater, including the installation. There are 12 issues of Service News per year.
:) :grin: