WARNING: This page is about a different car, the 2003 Nissan Altima. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Wiring Diagram - AUDIO - Base System (1 Of 3)
Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 2: Wiring Diagram - AUDIO - Base System (2 Of 3)
Courtesy of NISSAN MOTOR CO., U.S.A.
Fig 3: Wiring Diagram - AUDIO - Base System (3 Of 3)