Pioneer AVIC-F40BT 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 reverse gear is engaged. Unless
connected, the sensor may not detect your vehicle
travelling forward/backward properly, and thus the position
of your vehicle detected by the sensor may be misaligned
from the actual position.
Note
When you use a rear view camera, please make
sure to connect this lead. Otherwise you cannot
switch to the rear view camera picture.
The navigation unit
Power cord
Section
02
13
Engb