It is more than likely you do not have a illumination wire in the harness. I have a a Pontiac G6 which is in the GM Family and my wiring harness doesn't have a Illumination wire in it. so my installer had to connect the Orange/White Wire wich is the Pionner illumination Wire to my parking lights. Now when my parking lights or head lights are turned on the Display turns to night display and when my parking lights are turned off it turns to day display wich is page 92 in the manual. Also check to make sure your map settings for day/night dispay is turned to automatic for the display to change be
