My dad's 2003 GMC Sonoma has some problems with the rear drivers side running light. It does not light however the bulb is fine. I just replaced it with a Sylvania from Autozone. I also noticed that the license plate light is not working either. It is not burnt out as well. So there is basically no power to the rear drivers side running lights. Could this be a problem with the head unit where you turn the lights on?