Pioneer AVIC-F88DAB Manuel D'installation page 11

Connection
Violet/white (REVERSE-GEAR SIGNAL INPUT)
This is connected so that this product 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.
This product
Power supply
Power cord
Engb
Section
02
11