Lust in the Fast Lane(1984)

A young husband and wife goes out and their fuel is finished. They see a house and knock for help. the house owner promise to give them fuel if they become his guests for till next day. when they enter, their host's wife comes to the husband and host goes to the wife. she looks at husband for permission and he allows her. then they stay their and joins orgy with their some other guests. At the night when boy is alone he see they all came to his room. But for his surprise they were all vampires and his wife had also become one of them.