Depress the button on the seat belt buckle. If the belt does not fully retract, pull it out and check for kinks or twists. Then make sure it remains untwisted as it retracts.

NOTE
If a belt does not fully retract, inspect it for kinks and twists. If it is still not retracting properly, have it inspected at an Authorized Mazda Dealer.
Fastening the Seat Belt
Front Shoulder Belt AdjusterMazda 6 Owners Manual: To Resume Cruising Speed at More Than 25 km/h (16 mph)
If some other method besides the OFF/ CANCEL switch was used to cancel cruising
speed (such as applying the brake pedal) and the system is still activated, the
most recent set speed will automatically resume when the RESUME/
switch is pressed.
If vehicle speed is below 25 km/h (16 mph), incre ...
Mazda 6 Owners Manual: Rear door unit removal/installation
1. Remove the rear door glass.
2. Remove the inner handle.
3. Remove the rear door speaker.
4. Disconnect the power window motor connector, and power door lock actuator
connector.
5. Remove the rear door harness from the rear door unit.
6. Remove the bolts.
7. Remove the rear door lock act ...