My Partner the Ghost (1969)

Jeff Randall and Marty Hopkirk are private detectives who specialize in divorce cases. Their long-running partnership seems to come to an abrupt end when Marty is killed in a hit-and-run incident, but he is soon back--as a ghost--to help solve his own murder. In so doing he misses his chance to go to heaven, thanks to an ancient curse that states: "Before the sun shall rise, each ghost unto his grave must go. Cursed be the ghost who dares to stay and face the awful light of day." So Marty is stuck on Earth, as a white-suited spirit whom only Jeff can see, continuing their partnership and keeping (jealous) tabs on his widow, Jean.