Spockster is correct.
The fan is powered by the blue wire in the 10-pin connector. I think it is pin 5. Pin 5 is powered by pin 4. Pin 4 is always hot, powered from pin 1, from the battery, through the main 30amp fuse. (confused yet?). when the fan switch (lower left corner of the radiator) gets hot enough, it completes the circuit to ground, which triggers the fan relay to complete the pin 5 circuit. when the pin 5 circuit is complete it is also being feed from the main 30amp fuse.
So your friend should start by grounding out the fan switch. If the fan kicks on, then either the fan switch or the connection to the fan switch was bad. Either way, the positive power to the fan and the fan relay are fine. But if you connect the fan switch wire to ground and the fan still doesn't come on, start tracking down the blue wire in the 10-pin connector and the black/yellow wire (also 10-pin connector) to the fan relay. With the fan switch still grounded check to see if there is power on the blue wire at the 10-pin connector. if there is, then you have a short somewhere on that blue wire. if not, your relay is bad. if that is the case, i would follow the black/yellow wire on pin 4 just to make sure it wasnt cut or something and not allowing the circuit to complete. if the wire is cut or something, then maybe your relay is still good. the relay wire being cut is unlikely, but its always good to check before going through all the crap to replace/work-around the relay.
Best of all this can all be done with the bike off. none of this is powered through the ignition, so no need to have it running.
I will also add, this is to the best of my knowledge and I have never claimed to know everything about everything. Just a little about a lot!