I've got one on mine and no idea.
It seems to be linked back into itself with the black wire ?
Not for tow bar harness connect, not big enough for usual 12n 7 core, normally picked up in jack cubby. 12s harness for fridge/charging leisure battery ? usually requires thicker, cables although not sure what's in the sheathing.
Shorter answer - don't know, but like you, hope somebody does !