System Outline

When the light control SW is turned to TAIL or HEAD position. The current flows to TERMINAL 3 of the light failure sensor through the TAIL fuse.
When the ignition SW is turned ON, the current flows from the GAUGE fuse to TERMINAL 8 of the light failure sensor, and also flows through the rear light warning light to TERMINAL 4 of the light failure sensor.

TAILLIGHT DISCONNECTION WARNING
With the ignition SW ON and the light control SW turned to TAIL or HEAD position, if the taillight circuit is open, the light failure sensor detects the failure by the change in current flowing from TERMINAL 3 of the light failure sensor to TERMINAL 9, and the warning circuit of the light failure sensor is activated.
As a result, the current flows from TERMINAL 4 of the light failure sensor to TERMINAL 11 to GROUND and turns the rear lights warning light ON, which remains ON until the light control SW is turned OFF.