I use the radiator switch (bottom RH). Works, but I do have to watch the temperature reach 100C willing the the fan to cut in (e.g. when coming off motorway and queueing on the slip road). Dash-board temp. sensor is at top of engine block, so there will be a delay before radiator gets hot enough. Conclusion: it works but it may not be the best position for it. I also found that when my switch started leaking, the plastic holder had broken, so fabricated a new one from alu and all is good.
-steve