Demister / defogger not working

[durao]

Hi,

My Lupo rear window defogger is not working and the button is red lit even when depressed (it should turn yellow).

I have done some diagnoses already:

-The resistance wires built on the rear window are not broken and the multimeter current flows between the terminals when the power wires are disconnected.

-I have replaced the control button on the dashboard with one from other Lupo and the problem remained, but my button worked on the other Lupo.

I think there should be a relay behind the fusebox which should turn the current on when the button is depressed but unfortunately I don't know which one could it be.

Another possible cause can be a broken wire, but for now I will assume this is not the problem.

Do you know on which position is the defogger relay placed? There are around a dozen of them. A map of Lupo relays would be really great.

Thank you all for your support.