Michael A. Terrell wrote:
. . .
One of the engineers at Delco told me it was RG-62, and 93 ohms when
I was going to their annual car radio training back in the early '70s.
IBM also used RG-62 on their coaxial computer networking, but they used
BNC connectors.

The automotive coax I'm familiar with isn't RG-62.

Like automotive coax, RG-62 has a thin walled hollow insulating tube.
But RG-62 has a polyethylene "string" which is helically wound around
the center conductor to keep it centered in the hollow tube. The coax in
every old automotive installation I've seen lacks this PE "string", so
the center conductor is free to flop around inside the hollow tube. The
effect of the "string" is to make RG-62's Z0 constant and predictable,
and it will also increase the capacitance somewhat. Constant Z0 isn't
important for the automotive application, and low capacitance is important.

It seems to me the center conductor is smaller in the automotive coax
than in RG-62, also.

Roy Lewallen, W7EL