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So here is another idea or 2. I designed (but haven't built) for my 86.5 a simple analog replacement hvac control (cosmetic details TBD): I shelved the project when I found some minimum quantity requirements for a couple of the parts.
Some time later (a long time later), I looked at my F350 HVAC control (image from eBay). The interesting thing about this control is it uses vacuum to directly operate the diaphragms, no electric solenoids :
Then I googled "porsche climate control" to see if I could find the EL unit the OP posted a pic of, no joy, but I did find that the Porsche Boxster used a control a lot like the F350's, which led me to google "behr climate control" and paydirt- that faceplate design is used in a lot of vehicles, so maybe with different ***** it might fit in pretty well in a 928. They are cheap on eBay (I bought 1 for $15 to play with. And still playing with it...)
If that design floats your boat, I would say "have at it"! Pretty easy to find, and they more or less fit! Will take some work...
Ah so, let me expand: there are two issues, first, reverse-engineering the Ford (or whatever) vacuum connections. That's really pretty simple, and you can use the Ford vacuum harness and plug and adapt it to the 928 lines. Shouldn't be too hard The blower switch and temp control shouldn't present much of a problem , but then the electrical switching that is in parallel with the vacuum control (i.e., the same **** controls both) needs to be figured out . Obviously, I have done none of this. Just too lazy. If I ever return to the project it will be to use someone else's ideas, or go back to my original design, if I want to throw a few bucks away.
But I am going to fool (word chosen carefully) with that EL setup you posted. (Obviously Euro, and since a pretty good image search didn't turn it up, a one-off or very limited aftermarket.) Can't be that bright though, needs a filter...