OK now I've calmed down, a few observations from the land of total electronics armaturehood.
Who knew the S15 had a TV tuner? Although the frequency ranges just about overlap, alas Japan broadcasts using an encoding called NTSC-J, not PAL, and probably a different number of lines.
There's no obvious signal to the display unit to raise/lower the screen, unless they're the unreadable ones. Mine comes up pretty much it feels like it, so I assume it isn't simply in response to getting voltage on ACC.
The presence of two sync signals (I guess ?? sync might be vertical sync) makes it look to me like the screen takes an analogue video signal (I am not an electronics engineer). The RBGHV system does this. Systems like this are used in VGA and SCART (component video like from a DVD player is YPbPr with no separate sync).
"Video picture signal" is a bit confusing.
Does anyone know what a "Vicon" unit is? It seems to sit in or close to the boot lid and have a large connection to the TV tuner.
There's a separate mono speaker for the satnav voice commands (at least), to the bottom left of the steering column. Always wondered what that grille was.