Radiator Temperature Sensor

[jeffluent]

My car has a sender unit next to the top hose inlet which is not attached to anything.I left the car on tick-over until it reached 100c on the temperature gauge and the fan did not kick in. I can't see a stray female plug anywhere. Where should I look? Another possibility of course is that this is a scrapyard radiator from another model,there is evidence of a minor bump,and the fan is controlled by the ECU. In this case it could be a relay which I gather can go crusty.First thing I did was check the fuse of course.All advice welcome.

[jeffluent]

Further to Rad sensor.This has nothing to do with the fan problem.The rad has been replaced at sometime with a rad of the same size and fittings from a 307 or 407 or whatever that used a sensor in this position. If I had thought on,if the sensor was unplugged the fan would run continuously.Problem is a wire going into the relay box which has become brittle and snapped.Plug it goes into badly corroded as is the top relay. The easiest way looks like a scrapyard fan loom. QUESTION.I think this might be a two speed fan (aircon) so there must be a resistor somewhere.Any idea where anybody?