tailgate glass alarm fault
 

Hi All
The alarm on my C30 keeps going off.
Diagnostics by Volvo dealer indicates "voltage on the glass breakage circuit is not equal to ground ..... "
Presumably either the wiring or the sensor is at fault.
Does anyone know where the sensor for the tailgate glass breakage is located? (Does it use the rear screen heater element as the sensor?)
Thanks for any help ... the dealer wants to fit a new tailgate!!!!!