Did you get anywhere with this issue? I'm having the exact same issue myself with the same interface cable, in reverse the display shows sensors but not camera image.
Details below:
VW T6 Factory fitted Discover Media stereo, reversing camera and SWC
Kenwood DMX7722DABS with Connects2 CTUVW03 Infodapter
All other systems and adaptors fitted and working (with the exception of the Pink speed pulse as there is no input for this on the Kenwood, is this only needed on SatNav stereos?)
The factory reversing camera was definitely working on the factory stereo but for some reason no image comes up. I definitely had the interface cable connected correctly but to be sure I removed it and the blue connector and connected them directly for the photos (I tried both orientations just in case it had been wired incorrectly). If you click on the rear camera it's a blank screen.
On the Kenwood there is no settings for NTSC/PAL so I assume this will auto detect.
Any help would be greatly appreciated
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