This is not true. All 12V Mopars of this era use a dual filament park/ signal bulb, same as tail/ stop/ turn bulbs, 1034 or 1157. IT IS NOT powered unless the headlight switch is in "park" so you are correct, they are not powered with the headlights on, but they are still same bulb
ON a side note, all "Ma" did when the later cars have headlights/ park lights both on, is move the park wire over to the "tail" position. Later cars use same HL switch, just the P terminal is unused.
