Greetings Safari Bob!
Your coach was built during something of a transition year as it was the first year for the Univolt and the coach retained some of the pre-Univolt wiring features as well as advanced to the familiar 12-volt wiring for all lighting.
It sounds to me like your coach may have the original PAR (Peters and Russell) water pump. Should this be the case it may be connected to a transformer that steps household current down to 12-volt DC when connected to shore power or passes 12-volt power through when boondocking and operating off of the batery -- this is also how the electric fans in the roof vents, the range hood roof vent fan, and the furnace blower operated on the 1964
coaches. My undertanding this was a one-year use of this methodology -- and is also why we have the shore power/12-volt switch in the one-stop service compartment.
Good luck with your investigation!