How to Replace a Volkswagen Jetta Climate Control Light Bulb | More info
This video shows how to make your air conditioner/heater knobs light up again. All three knobs are illuminated by a single light bulb behind the center knob. Replacing that bulb will make it so you can once again see all three knobs when driving your car at night. It's very easy to do and only takes a couple of minutes.
I believe that some Passats and Beetles use the same climate control unit. If the one in your car looks like the one in the video, then this video shows how to change that light bulb.