How do I change the bulb that lights the heat/ac controls on my 2004 Jetta

You need to set the fan control knob to #2 position and pull the knob off. Get a pair of needle nose pliers and extract the bulb. Take to the auto store and get a replacement.

Start testing wires start from the end of the light bulb and go from there

Is that the one in the rear window center? If so you need to go into the trunk and up undernieth where the light is mounted you will see where you pull the bulb out. Once you pull out the bulb it will be connected to the wire still. Gently hold the wire end in one hand and with the other hand push in on the bulb and twist counter clockwise. It should turn and come straight out. Replace with same new bulb by just following these instructions in reverse. I hope this helped,
The Raz

You need to pull off the knob and get a pair of really thin needle nose pliers in there to extract the bulb.  Match the bulb up at a parts store or the deal and install opposite of removal.

sounds like the problem i had with my 97 subaru the lights were out for the fan switch and buttons for heat postions, i had to replace all the bulbs they were burnt out.

If you pull out that knob assembly that controls the drivers side heat behind it you will see little black clips that hold in the bulbs.But if you dont the bulbs are inside the controller and it will have to be disassemble to change them...

I’m happy to assist further over the phone at https://www.6ya.com/expert/joe_a3369546f8067589

Behind the AC control panel is a small light bulb, u will have to pull the panel out and replace that bulb, the bulb is mounted in an equally small twist in socket, u can buy the bulb from VW or most auto parts stores like NAPA or Carquest.

You will need to replace the whole in-dash A/C control unit. Changing the small bulb won't rectify your problem, as the display is LCD.

Replace the bulb. It's very small behind the fan switch knob. Pull off the knob and pull the bulb straight out to replace.

are the head lights turned on