Did these radios have these plugs because of the Windcharger systems they where often powered with. My Great Grandfather Billings had such system at his ranch in Cody Wyoming I don't remember the details, in 1960 it was a derelict system. But his was a Zenith setup with a Zenith branded Windcharger system, Zenith owned Windcharger. My Dad told me when it was in use it not only powered the radio but thanks to it's batteries was used to power a few 36 volt electric lights. At the time I remember there was still a number of Windchargers still on towers unused. Sure wish I could go back in a time machine a pick up a few of them.