Key Switch And Ignition Knob Switch

Check continuity between terminals 3 and 4.

3 - 4 

When key is inserted to ignition key cylinder : Continuity should exist. 

When key is removed from ignition key cylinder : Continuity should not exist. 

Fig 1: Identifying Continuity Between Terminals 3 And 4

Courtesy of NISSAN MOTOR CO., U.S.A.