308 SW heated rear screen not working

You still having problems since last years post ? I am not an auto electrician , employed others to do that side but any HRW I have fixed all had 12v at screen . I do remember on some Fords there was a problem with the earthing which was done through the tailgate hinges to body . It was resolved by spraying with WD40 , loosening very slightly and tapping back and forth with a hammer which made new connection for the earthing . Now I think about it , may have been the hinge pins that also completed the earthing . You wont get the right / any voltage if no earth , as already suggested previously , test wiring / earth at top of tailgate or run a good temp wire or tap and see if it fixes it . Probably need the engine running for testing HRW