My dad installed a radio in his car in college, in 1932 or so…
I dunno. As far back as I can remember, radios were always and add on accessory until recently when cars were packaged. First car I can remember was the 54 Ford that had a radio but paid extra for it. I think heaters were also an optional item back then-but really not much of an option in Minnesota.
We used to take a boombox in our beater car as a teenager. Had to hide it under the seats.
When I was young the family car (truck) was a Chevrolet passenger CarryAll. Since it had only one brake/tail light on the left rear door, a device was attached to signel turns. It was a reflectored vane like a railroad traffic signel. The vane laid down when not in use; went to straight out for left truns; and upward at a 45 for right turns (as hand signels would be done). I don’t remember how it operated but I doubt that other drivers would ever notic the signel eveen if they understood what the signel meant.