The ECU'S are really hard to get hold of 2nd hand. Everyone has the same problem of water damage. Plus there are at least 3 different types of ECU. At the moment I'm thinking of modding a similar ford module or even buying a universal central locking system and adapting it to use the Gal wiring has anyone tried this
If you've got air con then the air con fan will be on most of the time when using the air con . If you've recently added water you may have an airlock check to see if the coolant hoses are the same temperature . If not let the engine cool turn the heater onto hot remove the coolant cap and gently rev the engine to remove the air . You should also check the strength of the antifreeze if you've added neat water
The permanent live is usually a red and white wire. It maybe easier buying a Harness adaptor there only a couple of quid of flEBAY . You can run a wire to the battery but make sure it's the right gauge and fit an inline fuse
Have you tried giving the cooling system a good flush with a good quality flushing agent . Also check the fan is cutting in at the right temperature diesels are notorious for seizing fans . I wouldn't recommend a cooler thermostat because all your doing is hiding the problem instead of curing it. If all else fails there are additives which you can add to the cooling system which lower the coolant temperature