I added an electric fan as the car has been getting rather hot, a proper rad has arrived from Fred and is going in shortly but I'll keep the electric in case.
Now, in my Land-Rover 90s I have electric fans. Air ram alone is enough most of the time but when off-roading the fan is needed. In both trucks the fan is controlled by a relay. This relay is triggered by a thermostat in the water system. I also have an over-ride switch to trigger the relay manually if I think it's required. When the relay trips, I have rigged one of the spare lights in the Land-Rover dash panel to light up so I know the relay is tripped and thus the fan should be on.
So, what do we have here? The same. The middle switch supplied by Fred in the over-ride switch. The Demist light is my indicator that the relay is active, my car does not have a re-screen demister. The Haynes manual did not detail the pin out for the dash multi-plug and in my case it's only wired for the indicators, main beam, oil, ignition, fuel, temp and back lighting. Nothing else. So the bulb is powered via a direct connection and earths though the dash. I tried the un-used handbrake one but that back fed into the ignition and oil lights.