Mitch166

I would guess the temp sensor has failed. To prevent overheating someone has shorted it out. Sometimes people put a switch in line so they can switch the fan on and off themselves (why they don't just replace the sensor is beyond me). Find the sensor, check for open circuit when engine hot. If yes, sensor knackered. New sensor to fit. If the bodged wiring is easy enough to put back to normal, do so, if not, cut into the circuit and run it through the new sensor (it's just a thermostat switch)