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: Electrical parts
Battery cable
Before disconnecting connectors or removing electrical parts, disconnect
the negative battery cable.
Wiring Harness
To remove the wiring harness from the clip in the
engine room, pry up the hook of the clip using a
flathead screwdriver.
...
Mazda 6 Owners Manual: Vehicle speedometer sensor removal/installation
Without ABS
1. Disconnect the negative battery cable.
2. Remove the battery and battery tray.
3. Remove the air cleaner compornent. (See INTAKE-AIR SYSTEM
REMOVAL/INSTALLATION.)
4. Disconnect the vehicle speedometer sensor connector.
5. Remove the vehicle speedometer sensor.
6. Apply transmi ...