1996 Mustang GT power seat help please!

You should use whatever fuse is called for for that circuit and not one higher or lower -look at the fuse diagram to find it. The fuse was blowing because there's a short somewhere or the motor was drawing to much current - probably the latter since it would just blow every time if there was a bad short.

Check the seat track and make sure there's nothing preventing the seat from moving freely - something under the seat blocking it or something wrapped around the screw drive. Extra load on the motor will cause it to draw more amperage and can blow the fuse. The motor could just be burned out too.

Check the motor circuit for conductivity with a ohm meter and then check it ground to see if it's shorted. I'd open up the control switch and check downline from there. If there is no mechanical blockage of the seat on the track, then it's probable the motor. Get 1 from a junk yard.

Good luck!