Just in case it is useful for anyone like me who is using Grant Francis' system for controlling an electric main cooling fan (replacing the belt driven OEM one).
In brief, Grant's system makes the OEM small fan come on with the aircon compressor, and uses the water pump inlet OEM thermostatic switch to control thre main electric fan via a relay.
My problem has been that in traffic, the OEM switch which is set at 85°C does not have enough of a gap between on and off temps. So after a stop in traffc, a surge of coolant as the car moved off triggered the fan (either off or on) and then almost immediately switched it the othe way again as coolant circulated. This resulted in the fan switching on and off in a few seconds which does it no good, and in prolonged traffic this might really damage it.
The solution was a 22mm threaded switch that turns on at 90° and off at 85°. However this is a VERY hard item to find. In fact I imported a Tridon brand one from Australia as I could not find one up here. It works absolutely perfectly.
However, recently I have found one in Europe and this is the reference:
Brand MAHLE or BEHR
Car model it was used in CITROEN
Reference TSW 7D
number 70808438

typical link:
https://www.autodoc.co.uk/mahle-original/12236492

But a search on the referece numbers brings up loads of hits.