Germany – wire 3 core garage to 4 core mains

We have an external garage and a 4 core (brown, blue, green/yellow, black,) cable is supplied from the main property. The garage is supplied with an electric door opener, wall sockets and an internal light. The cable in the garage is a 3 core (brown, blue, green/yellow) cable that needs connecting.

I assume (need to measure) the black wire is connected to a switch in the main property. As I will not use this, I'm wondering the best way to handle the black. Should I just connect this to a connector block and leave it at that?

Thanks for any pointers