Thanks to specialist help from a generous fellow member I’ve now managed to connect the “Direct” camera and produce pictures on the Alpine.
A Multicomp Pro shell for the short lead to an RCA socket fits beautifully into this little 5-pin Direct Camera socket in the particular adaptor harness used in the 25AE between its Alpine head unit and the Mazda NC standard wiring connector.
Picture of test fit of the new shell in and out of the socket before I assembled the contacts needed onto a stub of coax with an RCA socket on the other end.
This phone pic is while the reversing camera I plan to use is still being hand-held inside the car while wrestling with the Alpine software to make it believe there really was a camera connected! Up to this point I was almost ready to give up on using the Alpine screen for a reversing camera.
And by the way, those 2mm contacts are just a bit fffiddly if you don’t have the tiny correct crimp tool.