BATT CHG switch function on 1972 Newell

[sopicki]

Hi all, I have a switch on my dash labeled BATT CHG and it has 3 positions, FRONT, OFF and REAR. It only has one wire going to it as the other wires have been broken off, eaten off or melted off at some point. The one remaining wire runs to a solenoid located under the floor access panel just in front of the front passenger seat. This solenoid has wires on one side that go to the rear battery and wires on the other side that go to the chassis battery. I assume that this circuit was to allow charging of one battery or the other but from where...the alternator? the converter? Does anyone have a Newell manual that states what this switch is supposed to do? or a schematic? Thanks!!!