This is a 7 pin DIN audio cable which attaches to the Harley-Davidson Boom! Audio unit and allows connection for wired (or wireless) headset. It allows a connection like that which comes standard on the Ultra models. Included is a Sena 7 pin DIN to 3.5mm Aux connector.
Here's a picture of the two cables and the equivalent 7 pin DIN that Harley sells.
Yours for $40 shipped.

 

Is this still available?