I just replaced a head unit in my 2002 Diamante. I can not remember if the controls for the ac light up or not. Mine do not and I dont know if they did and dont now because of something I did during head unit install or they just are not made to light up. Anyone know the answer to this. Thanks for helping.

Yes they do light up , the screen and the surrounding controls. The screen has a dimmer feature when the lights are turned on, wut yu can do is at night or cover the screen and turn the parking lamps on and see if the screen dims, if it does not , one of yur plug ins may be loose. If it does dim then the bulbs are burnt.

Could it be a fuse? If not how would I go about changing the bulbs?

Does the LCD panel that shows fan speed and blower direction dim when yu turn on yur parking lights? It would not really be a fuse if all of yur other instruments lights are lighting up , like the interior gauges lights. Like i said if the lcd panel is not dimming when yu turn on yur oarking lights the input for the lights may be loose. Replacing the lights is a so so job. Since my headunit setup is slightlly diffrent , but i think the bulb placement is the same. Remove the head unit, , where the rear plug ins ections id yu will be able to see the , i cant explain it , if yu ever changed the bulbs for the P-R-N-D +/- indicator in the instrument cluster , the bulbs are like those even the bulb retainers. Sorry i do not have apic of it, but its not that hard a thing to look for since yuve taken it out before.