The Return of October (1948)

This is the warm-hearted story of a wholesome Terry Moore, whose late uncle Willie (James Gleason) is reincarnated as a thoroughbred horse. At least, as far as Ms. Moore is concerned, he is. The horse's name is October. Moore is tried for insanity, then becomes the subject of a book by a top psychologist (Glenn Ford), who falls in love with his subject.