The heater/AC control panel lights have finally stopped working. I could get them to come on by moving the temp control lever back and forth a few times, but now that won't do it, either. The lamp that shines through the little hole, just above the "ash-tray" still comes on, so there is power to the area. I am assuming the filament(s) are broken. How do I open up or access that area to remove and replace the burnt out bulb(s)?