07 DTS All headlights work fine during the day. Both headlights will stay on all day. No blinking or shutting off. As soon as it gets dark the drivers side light will go out. I've changed the headlamp, the ballast, switched the passenger to the drivers side. Nothing is working. This has been going on for over a year or 2. I just noticed about 2 weeks ago that the lights work fine during the day when I had my wife follow me while driving the DTS. Any help is appreciated