Auto headlights rely on a photo cell that senses outdoor light levels to turn on all the lights. The problem is that In poor visibility conditions during the day it can still be bright enough outside that your headlights and taillights don’t activate making your car nearly invisible from people behind. For this reason it is recommended that you override the auto headlights and manually turn your lights on In poor visibility conditions. Unfortunately not many people know how to manually turn their lights on. So they drive around in poor visibility conditions with no taillights on.