Am chasing this problem currently.  1990 Legacy blows fuse #15, taking out power windows, tach-gauges, AC, and seatbelt.  Problem pops up every couple of weeks.  Have repalced the fuse multiple times now with no identified common cause.  I think I have found/checked all the grounds and connectors along this circuit, but haven't found a good wiring diagram to be sure.  Wiring resistance reads normal, and wires apear in good shape.  Any suggestions?