Its not that difficult on a 123...
Take off the wood panel that surrounds the climate control buttons. Then unscrew the black climate control package 2 screws, the third holds on something else. Pull this out and look agains the back wall. You will see something that looks a little like an octopus. In the center there is one lightbulb, going out the sides are little black wires, that are actually fiber optic, and go to the switches above. Either the bulb is burned out, or somehow the wires came undone. While you have the black plastic box in your hand, (the one with all of the buttons), you can check it for burnt bulbs too. There is one that can get rather warm, and slide out of its spot.
Hope this helps.
"...rationality of thought imposes a limit on a person's concept of his relation to the cosmos." -Nash
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09 Jetta TDI