MarkTemp Sensor wires
The Brown/Black wire to the coolant temp sensor is the +feed wire to all sensors.
The Coolant Temp sensor is grounded directly via the engine
The Orange wire is the control sensor wire to the ECU that monitors the resistance in the water temp sensor.Fan Relay wires
The Green wire is the supply feed to the Fan Relay
The Pink/Blue wire is the control wire to the ECU
The Blue/white wire is the relay switched 12V supply to the Fan Motor How it works
When the ECU senses a change in the resistance in the orange wire from the Temp sensor, it then it grounds the Pink/Blue wire of the control Cct for the Fan Relay supplying 12V to the fan motor.
To check the Temp Sensor operation, see Chapter 16 / SubPage 74 in the Mk2 Service Manual.
To check the fan motor you need to supply 12V to the Blue/White wire.
See also Chapter 16 / SubPage 62 in the Mk2 Service Manual.EDIT
The Fan motor will only run once the engine is running, when controlled by the ECU, as the fan Cct is not energised just by turning on the ignition switch.
Mk2 Document in one of the sub folders HERE
Hope this helps
to the forum