I hope this helps. I think it goes like this. firstly the 2 speed relay is located in the battery tray aea, behind the battery on a plastic pannel, the big green one is thefan speed relay, the other big grey one is for the heated screen (i think).
The switch is on the bottom of the radiator on the passenger side, it had a bosch multipin connector with 4 wires on it, 2 brown wires, 31-118c and 31-18b are ground wires (earth). The other 2 wires are brown/black, 31b53b and 31b51a are the speed control wires for the fans, they switch at different temps, to bring the fans on at the 2 speeds. Actually what this relay does is in the slow speed the fans are in series (slow) and at the higer temp the turn the relay over to put both fans in parrallel (fast).
To test the fans and the relay you will have to ground (earth out) the brown /black wires one at a time and see if the fans start up, one will bring them on fast and the other will bring them on slower.
The main fuse for the fans is one of the big 50A ones in the auxillary fuse box, wire no 30-27 red green, attatched to the battery positive post.
The fan motor 1 wires are + positive red/green 30-27a and - negative black/blue 54-34 The fan motor 2 wires are + positive black /red 54-31 and - negative brown 31-18, 31-18 is conected direct to ground (earth) 54-31 black/red goes to pin 7 on the big green relay, 30-27a red green is soldered to the main feed wire 50A feed in the loom somewhere so this is permenent live all the time, the other wire on this fan, fan1 the 54-34 black/blue, goes to the big green relay also.
The principal of the relay is that when the water temp reaches the lower level it brings on the both fans in series via one half of the relay, if however this is not enough to cool the engine then as the temp increases the other half of the relay switches on and puts both fans on is parrallel (the fast speed).
Also there is a 2 pin connector no.VC-2250 wire nos. 31b-12 brown/green and 31-23b brown, this goes to the aircon system. I dont know for sure but i think this will turn on the fans on slow speed while the air con is being used. The wire 31b-12 brown/green from the aircon connector goes to the large green relay and will be used as a switched live + to turn on the relay, in theory you could also put a live wire (temporary short) from the battery to test this part of the circuit, Lastly i have not tried any of these tests but from reading the wiring diagram i think this is how it works. Hope this is not to difficult to understand.