my son has a 2007 Lincoln mkz. when we bought the car one of the headlights was not working. i thought no problem the bulb is toast. after spending $ 110 on a HID bulb it still wouldn't work. after some looking around i changed out the ballast. this fixed the problem. after a year the other side had a light not working. same thing we changed the ballast and all good. we did notice that the rubber cover on the back of the light kept falling off. i have the car in the shop for an air conditioning problem and they noticed the drivers side headlight is out. after some testing they tell me that there is a short in the headlight assembly from water and debris getting in there and i need to change out the entire assembly. I'm currently trying to find a new or used light assembly. it looks like they made 2 styles of light units. my type is HID and the other is halogen. i am not able to find much at all in HID. is it possible to change things over to halogen if that is the only parts i can find? any other thoughts id be glad to hear them

