92 Deville blown fuse causing tranny probs.

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.