Take the wiring plug off the fan switch in the radiator, insert paperclip or piece of wire into plug you have just removed, to bridge the 2 wires together. (don't forget to have ignition on)

If it doesn't work, put the black wire of your multimeter to a good earth, and one of the pins in the plug that you have removed should have power. (again check with ignition on)

Try this and see what you have.