The movie came out around the same time as The Evil Dead (1981), so it probably came out between 1976 to 1986. It is an American film, in English and in live action and color, and it mostly takes place in Texas or a desert type of area. I watched it on VHS.
In the film a group of college students (both men and women) visit a place in a desert-like area. A little girl, presumably a witch, is shown pointing a bone towards their cars from far away while standing on top of a mountain.
When the students reach their destination and turn their cars off, they will not restart. There's a scene where a second car from the group arrives later, they try to keep the driver from turning the car off, but since he can't hear them over the music he turns it off and it wouldn't restart.
The students can't leave the place, and they use a book to cast a protection spell on the place. Later on a topless girl from their group tries to entice them to leave the spell of the protected cabin.
There's also a scene where the spirit of a priest or holy figure shows up. The demons convince the holy figure to "take them" and they combine into a big demon or some such.
There might also be a scene where a priest is standing and when he turns his back towards the camera he is naked from the back.