Ken Harper, 48, producer of the smash Broadway musical "The Wiz" which opened in 1975, ran for more than 1,600 performances and won seven Tony awards, including best musical. It was Harper who came up with the idea of a contemporary black musical based on "The Wizard of Oz." He hired Charlie Smalls to write the score and Geoffrey Holder to direct. The musical starred Stephanie Mills as Dorothy and Andre De Shields as the title character. Harper was executive producer of the 1978 movie version of the show which starred Diana Ross and Michael Jackson. At the time of his death, Harper was working on a new musical, "Bamboo," based on a Japanese folk tale. In New York City on Wednesday of cancer.