207 What is the free socket on the left-hand side of the trunk?

The socket extending to the rear by the front fuse box located under the left stop trim on my vehicle is idle. Does anyone know what it is used for?

I have no idea, unfortunately, but I was curious.

When I searched for the reference number, I am still investigating.

I will say that the type of installation that is made later is something, but there is a barcode on it that says psa or something, obviously the original.