'hold up'
I have got an aircon control panel
If we were to do a meetup- we could swap it in to check for 'some' functionality, which would establish if that was the issue.
I say 'some' functionality, because when I got the Cup in '02, one of the inherited faults was the lack of control of the temperature mixer-valve for the cabin-heater matrix. This was traced to a failed output line from the aircon control panel, and yours truly paid £700 for a new one to cure the issue.
HOWEVER- although the new unit could control the mixer valve; the rest of the firmware was bananas. the system would ONLY run with the A/C on and it kept doing it's own thing. Glenvarigill (at the time) tried to tell me that this was 'correct'- but I had a better idea; I had kept the old unit from the car, and had been inside it- spotting a large (socketed) PROM chip. I got Glenvarigill to open both aircon controllers, and swap the PROMs.
hey presto, as they say.
So I have a 'new' controller with an 'old' PROM in the car, and an old controller with a new, but bananas, PROM, in the house on a shelf.
I don't think it would 'fix' your car Needamaser, but it would do SOMETHING and that would tell us a lot about what had failed.
Can you post a picture of your unit...?
How it comes out is; you remove the stereo first; this reveals screws which allow you to remove the wider fascia. This in turn reveals four self tappers for the control unit itself...
I've got pictures of this, if you would like me to post them...?
(P.S- further to your worries about wiring- I have complete schematics for the Ghibli, from which the Spyder is of course related and I do technical wiring for a living)