Hi mentors

I've got a short question about wiring harness i've just received in order to retrofit my 2004 3.0 X5.
As you can see on the attached document, I did not understand what is the biggest black connector on the left side. JPuma'theme seem to not talk about this connector (certainly due to a different product version).
I've clearly identified the BM54 on the right side.
Thanks for your help.