2000 EU Corolla trip/on-board computer dead

#1
My father has a 2000 Corolla, EU-spec, the bug-eye facelift. Now, he has a mechanical speedometer (cable driven eddy current), but he also has a on-board computer for avg mpg, instant mpg and avg speed. This hasn't worked for a couple of years, I have swapped the display assembly up top in the dash, no change. All it shows is 0 or -/-.-.

What links does this setup go through from raw data to display? Might be related to it, but down below the AC control, the CD-player is. The stock Toyota one is gone ofc, Norway is the first country to CLOSE DOWN the FM radio and switch to DAB+.

But what I noticed is that there are more plugs, either up top or down at the CD player, than there are connectors on the display or the stock CD player. There is a 4 pin plug that just isn't connected to anything. Now this exact 4-pin plug is the same as on an Avensis onboard computer display. Tell me this isn't somehow connected...

Anything about this is greatly appreciated, even though not important, it has annoyed me for years now!
 
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