I've scoured dozens of threads to find a definitive answer but can't find a problem quite like mine.

I don't think my radiator cooling fans are working properly. The car is a P3 six - so has the twin set-up.

It's my understanding that when the engine is left to run up to 97 degrees Celsius, both the fans will kick in on low speed until the temperature reaches about 90 degrees. After having a look at mine today I've seen that only the left fan (looking at the front of the car) is coming on at this low speed. It does still bring the coolant temp down to 90 as it should though, which is reassuring at least.
I'm sure I've read that, to test the high speed operation of both fans, you should unplug the connector from the brown temp sensor on the thermostat housing. I tried this and both fans started working on high speed - and brought the engine temp right down past 90 degrees rapidly and effectively!

I'm assuming the actual fan motor on the right-hand fan is working OK as it's spinning up perfectly on the high speed circuit.

So, what would cause it not to run on the low speed setting, considering the left fan does operate as it should? There are various relays on the fan housing it would seem, could one of these be broken? Is there a way of swapping them around to identify a dud one?

When you say wiring, do you mean there's an individual feed to each fan? I've not looked that closely.

But considering that the right fan works OK on high speed, surely this means the 12v feed is alright?

Is it the case that there's different voltages applied to the fans to achieve the 2 different speeds do you know? If so I suppose this could be something to look at...