70s or 80s High School Slasher Backs Over Girl With Car

by Jay
(Tucson)

Years ago I watched a horror movie and I do not remember much about it other than this:

A bunch of teens/young adults are cleaning out an old school or are renovating it or something and there is a killer, killing everyone off. The only scenes I can remember are one where a lady is sitting in a car and someone slashes her throat from behind, and another where a girl is put behind a car and is backed over.

In the final scene the killer holds a girl in a box/cell of some kind and I think there winds up being a fire.

Can anyone help me with this one??
vague i know!!
thanks