I succeeded. The rear screen on my hardtop is heated. I found the wiring was plugged into the blank as described and it was easely put into the switch. I bought a new relay and placed it as relay 3.
What I did´nt know was that I also needed a 25A fuse to put into fuse 7 which was empty . At fuse 6, which is not in use, there already was a 25A fuse as a spare. It was simply to put it into fuse 7 and every thing worked.
Thanks for your help