Instrument Panel
 

I have a 00 ML 430 and I am trying to figure out how to get the a/c control display to light up. I have tried to turn the lights on using the same control that turns the headlights on but it only lit up the a/c control display.

You have a burned out bulb on the A/C console.

It's a dinky bulb (mine went out too), and you can get a replacement at your local Auto Zone or Pep Boys.

Carefully pull the center knob completely off, and you will see the bulb. You might need some tweezers or something to pull the bulb out, as it's nestled well in it's housing.

Replace the bulb, reattach the control knob and you're done!