I took the plunge and joined the grey and brown cables together onto one terminal of the fast idle solenoid and the blue/red to the other.
Now, for the first time since we bought it in 2000, we have functioning 2 stage cooling. Not that we got to stage 2 in today’s 20 mile test, but we know we have previously albeit only briefly.
Can’t believe that all this time all it needed was cables connecting and a fuse installed!
I’ve even managed to turn down the idle speed - the fast idle solenoid works.
Yay, today is a good day.