Sample operation: (When lighting switch 1ST position turned ON)

WARNING: This page is about a different car, the 2006 Infiniti G35. However, it is still accessible from the selected car via links, so may be relevant.

When lighting switch 1ST position is turned ON, contact in combination switch turns ON. At this time if OUTPUT 4 transistor is activated, BCM detects that voltage changes in INPUT 5.
When OUTPUT 4 transistor is ON, BCM detects that voltage changes in INPUT 5, and judges that lighting switch 1ST position is ON. Then BCM sends tail lamp and clearance lamp request signal to IPDM E/R using CAN communication.
When OUTPUT 4 transistor is activated again, BCM detects that voltage changes in INPUT 5, and recognizes that lighting switch 1ST position is continuously ON.

Fig 1: Circuit Diagram - When Lighting Switch 1St Position Turned On
Courtesy of NISSAN MOTOR CO., U.S.A.

NOTE: Each OUTPUT terminal transistor is activated at 10 ms intervals. Therefore after switch is turned ON, electrical loads are activated with a time delay. But this time delay is so short that it cannot be detected by human senses.