To check operation of the rear (1) STOP switch, use a multimeter: when the rear brake lever is operated,
there must be electric continuity between the terminals of the corresponding switch.
No electric continuity should be available when brakes are not operated.
Electric diagram
If these tests fail to produce positive results, the part in question must be replaced.
Gear/neutral sensor
The gear sensor (1) is positioned on the vehicle rear RH side, near the solenoid starter.