The relay is under the seat between the battery and the regulator/rectifier. The fan is the only thing on that circuit - it should be a 15 amp fuse and the fan should draw around 5 amps, so plenty of cushion there. Either the fan itself is shorting or the wiring insulation has rubbed and caused a short to the frame. It would be helpful to know if the fuse blows as soon as the bike is turned on or if it is when the fan tries to turn on. That would tell you if the short was before or after the relay. Also, does the fan spin freely or is it binding? If binding is it bearings or are the blades caught on something?
If the fuse blows right away it isn't a problem with the fan but probably in the wiring between the fuse and the relay.
2016 GSX-S1000F, Red/Black
2014 V-Strom 1000