I have retrofitted a reversing camera in my Audi A3 and diverted the flow of the reversing lights. Because the rear lights not clean voltage narrators (Pulse Width Modulation) verusacht this interference in the display. Remedy this signal filter smoothes the signal and thus provides a continuous constant supply. This signal filters you can (RC element) with a little know-how to solder together for a few euros itself who it likes but comfortable accesses here.
