Pre-Zombie movie set at a drive-in

I remember this movie was shown on the Late Late Show in the late sixties early seventies. I can’t exactly remember the whole plot, but it consisted of a teenage girl who happens to come across a guy she once knew or thought this person was the guy she once knew at a drive-in theater. Most of the movie takes place at night, I think because the guy has a problem about being out in the day. He always wears sunglasses and rarely speaks. I can’t remember what exactly happens, but the girl finds out that the guy has actually been dead and whatever she has been talking to is starting to physical decompose before her eyes. in the last seen she is trying to get away from him and he is trying to stop her, but she runs him down with the car at the drive in. I remember the movie was in the style of American International Horror film or very low budget with hockey dialogue. Anyhow, I can’t remember the name of this movie.