A recent discussion of radios in a B12 on the Lancia Club site brought to mid the restoration of the radio that was fitted to my 1952 B20. The radio was vintage Autovox, model RA15L, a substantial heavyweight from the time. Getting it restored was interesting: first, the main three vintage radio restorers in the US wouldn't touch it. but there was a vintage radio buff in Trieste (Italy) willing to take it on. Not so easy these old parts!
He had to hunt hard, but he was able to find a power diagram, and then even located a power source on Ebay, and proceeded to rebuild the radio in detail. writing up his work: https://www.depoi.net/en/2017/restoration-autovox-car-radio-lancia-aurelia-b20
And thanks to Ed Levin for finding more info, a site with the wiring diagram: