Maybe is specific to my car model (Nissan Xtrail T32B ) but I just connected the yellow video cable from the harness to the correct port. The harness even came with a special cable for this without the extra redwire for ACC:
The signal comes already processed with the reverse image and the 360 view:
12V power and reverse sigal comes directly from the rest of the harness. My original radio had a "DISP" button that allowed me to cycle to the front camera and the laterals but I´m not sure how to do this with the CC3.