spacer on back of engine has 2 sensors
brown and yellow
brown plug = black yellow / brown white is thermo time switch,

yellow plug = brown green to pin 21 black box

brown wire shares an earth with the aux-air device

the other engine coolant temperature sensor is for silver ecu
from what I can make out it maybe located on the thermostat housing
it certainly uses the same shaped plug as the sensor on thermostat housing on the s2
this is how I read the manual for s2 rs turbo

if it don`t make sense pm your number and I`ll call you