I fitting slim line fans for the usual reasons, Space.

Now the mechanical side im fine with, my problem is electrics! On the engine coolant fan there are two plugs, one is the power unit to the fan, Does anyone know what the other one is (upper plug)? Behind it is a coil of wire with a resistor and a heat shield. The same is found on the back of the fan power unit, and on the ac fan power unit.

Has anyone fitted slim line fans, or knows how to help?