On an 02 L the headlights have been changed to halogen and the driver's side is very dim, but not out. Have not changed the bulb yet due to thinking in the past of owning non halogen, they simply go out and you change them. Do halogens dim due to lack of voltage or ground or do they dim going out and need changed?

 

I've found that dim headlights are usually caused by a bad ground.