To fit the Parking Assist Distance Sensor, first join the O-ring spacer around the sensor membrane lip, so that the broad area of the O-ring touches the sensor casing and the narrow section faces outward with the sensor's back. After that, place the sensor into the sensor bracket on the rear bumper fascia, making certain the sensor membrane is flush outside and that each sensor centers itself in the openings without pinching the O-ring spacers. When that is done, secure the wire harness connector to the sensor connector receptacle in the back of the fascia. After you finish with the inboard rear park sensors, put the bumper fascia back on the rear and attach the negative side of the battery cable.