I recently purchased a '97 Cavalier LS Sedan 2.2 Liter as a spare vehicle, the car has 162,000 miles on it runs well and is in decent condition. The previous owner was not mechanically inclined and the car suffers from neglect. I am now in the process of getting it back into good mechanical condition but have become baffled by one issue. If I have the A/C running and press the button to turn on the rear window defroster numerous lights on the gauge cluster light up, the temperature gauge and tachometer dies. Is this an indication of a faulty heater control that needs to be replaced or could it be something deeper? Thank you for any help that can be offered!