Clive's spot on (10pts to Clive, no confering) that there are two sensors for climate control :-
- Sunload sensor - that's the small dome (like R2D2's head) poking up from the middle of dashboard just behind the windscreen. Mine appears to be a semi-translucent dull red when a bright light is shone from behind.
When I had the radio out (it was U/S) I don't recall seeing any wiring heading in that direction, but the top dash pocket may have been blocking the view.
- Cabin temperature sensor - located behind the small grill that's between the heated front and rear screen switches.
If you remove the switch panel then you'll see the grill is an opening for a small tube with a funnel shaped end(attached to the switch panel) that directs cabin air onto the temperature sensor which is clipped into recessed support bracket (looks a bit like the CND logo) about 6cm back from the front face of the switch panel.