Do you want the switch to switch +12v to the relay, or ground to the relay? Depending on what you want you wire it one of two ways.

With the switch sending +12v to the relay you do it as follows:
85- ground (not the one to the fan, just a ground in general)
86- switched +12v from the switch to turn the fan on
30- constant +12v from a reliable source, large awg wire (enough to supply sufficient juice to fan)
87- +12v to fan... again, with a sufficient awg wire


With the switch sending a ground to the relay, wire as follows:
85- switched ground from switch to turn fan on
86- constant +12v (easily jumped from term. 30)
30- constant +12v from reliable source, again large awg wire
87- +12v to fan... again, sufficient awg wire


As for which wire is positive on the fan, that's easy to figure it out. Hold one to ground and the other to +12v momentarily... if the fan turns the correct direction then you have it right, if it spins opposite of desired direction than switch the ground and +12v