SPH-DA120 reverse camera problems

[Brackens]

I've just installed the above head unit and a reversing camera that I bought from amazon. It all works ok when the engine isn't running but when you engage reverse with the engine running it doesn't automatically switch to the camera mode. the purple/white wire from the rear of the stereo is wired into the live feed to the reverse light, i've also tried using the ground and switched the polarity in the settings but this didn't achieve anything. Has anyone got any ideas?

[r5gtt]

Take the purple wire off and see what happens.

[MateyGuv]

Iv got the same head unit in my daily and had some issues with the camera. I had to play with the settings to make it work. If youv got signal when ignition is off its going to be one of the settings need changing 
Have you wired the handbrake switch as well?