Not sure for sure, if you don't get a clear answer before morning I'll drag some parts out of storage I think might be similar. Might be for the port for the throttle channel? Not sure that it would have come in the plane like that. I doubt the factory would use a 2 wire plug in a 3 wire connection.
*EDIT* I see its a 4 wire connection, and it was put in that way from the factory to power an FPV camera