Rear screen wiring

I've managed to pull through the tailgate wiring after much difficulty

Unfortunately the body shop pulled out the wiring before I had chance to picture it. The rear screen wiper is all sorted as is the connections near the N/S rear light - that bit is ok.

I've now got a black earth screwed under the roof frame about middle of car with a spade connector . I assume this is the earth for the heated screen on the O/S.

Then I've got a brown wire - guess the live with the remnants of a spade connector which I need to fix. I guess is this for the N/S screen heater spade. Then the mystery is a black wire without any connector or sign where it goes ? It comes out the black sheathing.

Can anyone help ?

Black isn't a ground usually.  Black is power.
Brown is ground.

But on my cabby, there are 2 black wires going to the demister white-to-black is the power side and black to ground is the ground side.  Your Brown may be main ground to the frame of the rear hatch.  I would look for a Screw hole that isn't being used.