removed negetive cable from battery post to clean corrosion. on 2006 Jaguar X-Type

Upon removal of negetive battery cable to clean post and clamp, a small connector appeared out of nowhere. It sits at the end two green wires and has a small green horeshoe shape on the connection face. I've looked for a connection site but I am stumped. What is it and where the heck does it connect to something?

Asked by for the 2006 Jaguar X-Type
Look on battery case/box. On the upper side of case, mid ways, the side towards driver.