I know we usually deal with mains-related subjects here. But anyway....(it is electric after all [Linked Image] ).

Does anyone know who and when these sockets and plugs for 12-volts DC were developed for cars?

[Linked Image from 12v-parts.com]

There's this one company (Safco is the name) that claims that they developed the type of plug currently in use, so I'm wondering if there were other configurations.

Was the use of the socket as a power source for a cigarette lighter also the first use of this thing, with the accessory plugs coming later?