1. Disconnect the back-up light switch connector.
2. Inspect for continuity between the back-up light switch terminals using an ohmmeter.


Back-up light switch removal/installation
Flasher unit removal/installationMazda 6 Service Manual: Dsc on-board diagnosis
On-Board Diagnostic (OBD) Test Description
(See ABS (ABS/TCS) ON-BOARD DIAGNOSIS)
DTC Table
PID/DATA Monitor Table
Active Command Modes Table
...
Mazda 6 Service Manual: Trunk Lid
WARNING
Never allow a person to ride in the trunk: Allowing a person to ride
in the trunk is dangerous. The person in the trunk could be seriously injured or
killed during sudden braking or a collision.
Do not drive with the trunk lid open: Exhaust gas in the cabin of a vehicle
is dangerous. ...