Headlight wiring problem

Hello. I own a 99 crown vic police package. The passenger side headlight suddenly went very dim. it still shines but is barely visible. I noticed that of the three terminals on the headlight socket, the middle one was burnt and the surrounding plastic had melted. Does anybody know what causes this and how it can be fixed? I'd really appreciate some help.

Look closely at all the grounds. Especially the one close to the battery. Usually a dimming light is indicative of a grounding problem