Pioneer AVIC-Z120BT Manuel D'installation page 13

Connecting the System
Violet/White (REVERSE GEAR SIGNAL INPUT)
This is connected so that the navigation system can detect
whether the vehicle is moving forwards or backwards.
Connect the violet/white lead to the lead whose voltage
changes when the shift lever is put in reverse. Unless
connected, the sensor may not detect your vehicle traveling
forward/backward properly, and thus the position of your
vehicle detected by the sensor may be misaligned from the
actual position.
When you use a rear view camera, please make
sure to connect this lead. Otherwise you cannot
switch to rear view camera picture.
Note
The navigation unit
Power cord
Section
03
13
En