Help us help you better...remember to give vehicle details like model/model year/build date. There are multiple changes that occurred during the production run...so in order to get the best suggestions/recommendations/answers/etc...having the correct vehicle model/mode year/build date/etc helps us give you the correct information. Without it, you may get information that doesn't pertain to your vehicle due to changes.
FWIW...the stuff behind the left panels in the cargo area are audio and telecommunication components. So the wiring harness you're asking about (and pictured in the last 4 pics above) are probably related to one of those components.
And it also looks like there's a lot of audio/telecommunication components missing or not optioned. Has the original equipment been removed and replaced with aftermarket components? If yes, then that would also be helpful to the forum in answering your questions about the wiring harnesses running through that area of the vehicle.
In your pic below...the wiring connector you're holding looks a lot like one of the CD changer connectors:
{e38/e39/e46/e53 CD Changer connectors}
