David,
If any of your light fixtures have 2 standard sized bulbs in them, one of
them will be 12V. Normally at least one light will be set up this way. Other
12V items found in my '60 are a vent fan (switchable from A/C to D/C), a
small porch light, the furnace fan - which yours won't have unless the
furnace has been updated and the pump. You also have the option of adding
12V power plugs if you wish.
Scott