Proctologically Violated©® wrote:

The ground, for the antenna, was at the base of the old style
telescoping whip. The ground connection to the body was through the
mount on the whip, where the mount gripped the hole in the car body.

Insulated? No, it was a plain mica cap. The screw on cap was probably
chrome plated brass ...

I have wondered if the "in glass" antenna on the cars could be replaced
with the old whip and what sort of tuning was available on the new car sets.

On my buick park avenue, there is, what appears to be, an active
antenna--it is a little plastic box attached near the rear view mirror,
compass and gps.

I have seen some car radios which have been removed from autos and the
terminal strips with all the wire connections do appear as a nightmare.
I'd certainly desire a schematic and pin-out to tinker with one. I
never bothered to look for the antenna trimmer though ... perhaps you
must remove the case these days?

JS