Somewhere in the head or a coolant passage near the head, there must be a coolant temperature sensor.
The North American versions around that year had either a 2 pin or 4 pin sensor. The 2 pin had 2 separate thermistors going to ground though the sensor housing. The 4 pin had the 2 thermistors going to diagonal pins with separate ground wires. One thermistor is used for the ignition module and the other (green/red wire) goes to the injection control computer.
Thermistor resistance at 20 degrees C is about 2.5K ohm.