I don't believe that the US S1 version has a ring terminal coming out of the forward harness. Should be easy enough to find though. Take a multimeter, set it to resistance (ohms), connect 1 probe to the ring terminal and probe each connector pin with the other probe. You'll have your answer in 5 minutes.
Now if I had to guess, it is a ground connection, But I would not hook it up to my bike until I was certain,
Both versions should be almost (totally?) the same. We do not have an immobilizer not ABS, but neither of those should have a connector on the headlight harness. Have any mods been done up front? A power outlet, USB , anything?
I agree, use an ohm meter between the ring and any black wire on the plugs. If you get continuity between the ring and other black wires on plugs it would be a ground wire that attaches to the frame of the bike. There's a high probability it's a frame ground for the headlight sockets so I would first test to see if that ring has continuity with the headlight plug ground wires. If you confirm this is a ground it would attach to the frame. If you inspect the frame you may find where it attaches to.