The Engine Bay Main wiring .. 14K733 may/may not support Heated Windshield.
If it does not support, and the car is a low series model, the receptacles for the relay will not be in the Fuseboard (14A073) If you PM me the VIN, I will tell you EXACTLY what wiring the car was built with (so long as the car's build is after 2001) and let you know if an upgrade is possible. Dealers can't do this, I'm afraid. It requires access to the specific build data (not just the minor features)
Failing that, you will need to get yourself a separate relay (I can give you the finis) and wire up independantly to a stock switch you could install on the Heating panel.

Cheers ......