What the heck is THIS ?

I borrowed back my old Subaru from John and Cynthia a couple of weeks ago when Ellen went to Swarthmore and I stayed home, but it does not have a current inspection sticker, so I don 't use it much. But I had to use it yesterday to get to a Pastoral Relations Committee meeting in Guilford because Ellen was in Northampton. On the way home it sounded like something was dragging, so today I gave a looksee. I discovered that a black, sealed plastic box that has several hoses and wires running to it had come loose because of rust and indeed was dragging on the ground. I have no idea what its purpose is. I hesitate to cut the wires it's hanging by because they might be hot. Anybody out there have any ideas?

                The mystery box

            Hoses and wires! 

       Where it's located-under the right rear fender in front of the bumper. The bolts that fastened it to the frame completely rusted out.