Scandinova frost free Fridge freezer?

Hi my Scandinava frost free Fridge model no Sff6745 serial no 23619448 the defrost termination thermostat no longer works and is no longer available.iwould like to install a digital temperature controller but I don't know how to wire it up can please show me how to wire it so the defrost heater comes on . please show me were which wires I take from the main thermostat and which wires I take from the defrost heater and fan .any help would be greatly appreciated.regard