I have a 2008 C350 and the daytime driving lights are enabled. Well at night, I like to have the fog lights one, so when I change the lights from the off mode to the on mode, the headlights turn off, but the fog lights do turn on. I tried deactivating the daytime lights, but that didn't work. So right now, my only source of lights is with the daytime driving lights enabled. Waht could this be, a fuse maybe?