Hi,
I just followed up that brown cable...
it it is connected to a kind of plug in the left part of the boot (behind the first aid kit)
its connected to the top "plug" (the cable is yellow in the end, they probably had a yellow cable with a lug that was not long enogh so they connected that to a brown cable)
top plug: its connected to pin 5, the other end of pin 5 is a very thin brown/black wire...
again, that's for the Belgian Polo. The cables might be different in a British Polo, because I was told that they are also different in a German Polo...