W208 convertible rear not demisting????

[mrroverrover]

I assume it's been asked before but yes I have searched and found nothing
My 99 CLK320 cab was all fine when I bought it 9 months ago but now the rear demister does nothing!
Switch lights up when on, mirrors heat up but the rear screen does nothing. Checked all 3 fuses it could be but all ok.

Where can I find the wires going to the screen or the relay for it?

Ta in advance

 

[mrroverrover]

168 views and not a single reply .
I'll assume no ones had this problem then? In the back with a squeegee it it's then!