you need to check the wiring.. it sounds like a wire is touching something it shouldn't be.. start at the rear defroster and work back.
I have a 92 4Runnser V6 SR5. Over a year and half ago I had the fuse block
> replaced underneath the driver side.
>
> Now I am recently having problems with my rear defroster fuse. The sucker
> keeps on blowing.. I put one in and as soon as I turn on the Rear Defroster
> POP!!!! The 20 amp fuse blows up.. I didn't have any problems before.. >
> Any ideas would be helpful in fixing my problem.
>
> Thanks,
>
> Billy
>
>