Three wire box behind P.S. Booster.Black yellow red. Defroster button pushed. Fan blowing.Black wire 0. Red wire 12v. Yellow maybe I'm thinking 4v. Ground wire to make fan operate still hooked up at test time. Are you thinking that the speed regulator is kaput? Still in working world so takes a while to get all tests conducted. Also might add fan blowing with much effort but not much air blowing inside. By the sound of it , it should be having more force inside car. First time the fan was started ,mounted in bracket, and no shrouds on lots of force blowing up toward hood. Did I say lots of force? oh boy. What are chances that the fin direction is wrong? Seems to be oriented like the old one was.