The sensor in the middle of the dash is called the thermal load sensor. It tells the bcm heat and light loads inside the car. I will look up diagnostics for this tonight when i get home. This turns on the lights and has air conditioning control. Sometimes when it gets too hot inside my car the air conditioner shuts down until I open the windows and drive the car. What year is your car?

 

It is called the solar sensor it controls the automatic headlight functions and is an input if your car has automatic air. It is an input to the bcm on circuits 1137 5v high and circuit 1138 solar sensor low.
When you say the dash lights up what do you mean? Do the dash lights turn on or do all the warning lights come on? And still what year and what type of air conditioning do you have?
The bcm controls most cluster functions as well as security and automatic lighting functions if your car is new enough. It also depends on trim level as to what options your car has. By the 2000s car are pretty advanced with multiple levels of computer controls and require advanced scanners to diagnose.