Next I turned my attention to the wiring. The old owner's radio has a different, US spec connector than the European ISO 10487 that turned out to be required by my German radio find (and which I suspect was original to the car with a Becker or Blaupunkt or something). I had to order a correct one - again with guidance from a friendly Pelican.
The existing wiring from the car on the right, new connectors on the left. Heat shrink crimp terminals from Amazon to splice the wires together, left. Combo crimp/strip tool is vital.