this is really an old thread... the "coolanf level" function is controlled by the LCM - accross all models, petrol/diesel, left/right hand drive, from 09/99 to 09/06 (the entire production run of the car) the coolant level switch (S63) is wired to a pin 24 of the 54-pin connector of the LCM.

The LCM is monitoring the switch - if the line is "grounded", there is enough coolant, if the line is "broken", there is insufficient coolant level...

Theoretically, if the switch is not wired for real (I doubt it), one can run a single wire from Pin 24 of the 54-pin connector (X10117) from LCM to Pin 2 of the level switch and have Pin 1 connected to ground point, and have a functional coolant level feature... however, i suspect, that once you get to the LCM and look at the Pin 24, you will find the pin slot already occupied - if you know how to trace the wires, you will find the other end tucked exactly where X5SND mentioned... why it was done so? beats me!!! but it can be fixed...

my $0.02