Peaty, Just went through this on my GT. Here's the step by step instructions I put together. Hope this helps!
Hey! Got those heater/AC lights working! Just wrote about 100 words to describe and my ham hands hit wrong key? Bam, gone!! So here goes again. If you got the 1st one, I'll recover here and finish. The lighting includes backlit mode select buttons, green lights showing selected mode below the buttons, lit slider control and fan switch and fan speed surround. All run off 3 bulbs! A/C has it's own inside the button (another story) First remove the Cup-holder (2 screws) and then pull out the top vents and surround. It just pulls out. Grasp it at the bottom of the vent openings and pull. This exposes the 4 screws holding Heat/AC module. It is held in then by temp control cable. This is held on by two locking rings, one on the cable end and the other pushed into a groove in the plastic, capturing the cable sheath. Both can be pulled out with long-nose pliers. Be patient and don't damage anything. I released park brake and sat on center console to get at it. Once loose take the module to workbench. The circuit board is covered by a sliding piece of black plastic which releases upward. The three bulbs turn 1/4 turn and pull out. There are 2 short and 1 long (lower right).The low center one may require you to release two catches and slide the assembly apart enough to get at it. (careful !) I would purchase all 3 (about 10-12 bucks) slip 'em in and put her back together. Wish someone had explained this to me first! The circuit board cover took a while to figure out! Dumb!! Good luck! Gives you nice opportunity to detail the buttons (pop off from bottom) and clean up the vents too! Happy GT'ing!! Glenn