Ihadmytaintamputated

I have an 06 530xi wagon N52 auto I just picked up cheap and I'm working thru the issues but I found a black wire with a small square box on the end, which has a copperish lug with a hole thru it, and opposite side has a stainless looking coarse threaded lug sticking out. There is a number printed on top of it as well seen in the pics. This wire comes into the void above the Battery tray area behind the panel passenger side, above the flooring and from somewhere towards the seat hinge maybe?
- What is it? Where/what does it bolt to and what bolts to it?
- What system does this belong to, I'm having the usual electrical issues and beginning to chase thru them now, starting with it raining and flooded the modules out back. Pulled and stretched them up into the void above the battery tray.
Im about to start the hinge wiring repairs, should I wait to reconnect whatever this is until after I complete the wiring repair?
thanks in advance... I'm in a wheelchair currently and can't just rip all the panels out and track it down easily.