So I've got this little box that I knew was there, but haven't bothered with until now. It came with the car.
Its hooked up directly to my headlights, replacing the factory plugs, and it uses one of the factory plugs to know when to switch on/off. I put the factory plugs back into the headlights and everything works fine. So obviously it's not there to replace stuffed factory headlight electricals.
I've since removed it and all 100ft of loom that came with it, but wondering why someone would have put it in in the first place?