I recently developed a problem: When I turn on my defroster, it blows a 15amp fuse which, in turn, causes my transmission to lose all but 3rd gear while driving. I can manually shift 1st & 2nd but overdrive is completely gone. When I replace the fuse, everything returns to normal until I turn on the defroster again. Does anyone one know what the problem is?

Well overdrive is generally a solenoid activated gear. As for blowing the Fuse something is drawing too much juice.