Also, there is no mention of connecting any wire from the radio
directly to the battery for a continious power source. The main lead
(red wire) is supposed to be connected to +12 switched. The old radio
(that I removed) had a wire connected directly to the battery with a
small plastic fuse casing in the middle. Do modern radios use a
different method to maintain memory when the power is switched off?


In UK there is often a constant 12v feed which if disconnected requires
you to re-enter the security code for reasons of anti-theft. Maybe your
old radio had this feature, or just needed power for the memory & clock.