I used the std temp switch and used this to trip the relay NEGATIVELY so that it runs on after switch off if necessary as engines get hotter(water) after switch off.
Im then put in and overide switch in case of temp switch failure so it could be switched MANUALLY, this of course has to trip NEGATIVELY so used another relay but fed it with NEGATIVE instead of POSITIVE through the LOAD terminals, this only remains LIVE while ignition is on so fans CANNOT BE LEFT ON.
tabetha