I have a 99 blazer. I recently installed a boss bv8965b head unit with a 7 inch screen. When i tutn on my headlights the screen turns blue with the word "car" in the upper left hand corner. Music still plays but none of the buttons work. We have checked and rechecked the wiring. Im stumped. Please help.

 

Turning on the headlights applies (most likely ground) from the BCM to the radio, through the purple with white stripe wire to dim the LED display in the radio. Whatever you have that wire connected to on the head, is not where it needs to be.