Problem with Camera or Block?

Question

Electronics

Maybe I'm asking in the wrong group, but
there is a Screen with a control unit and there is a Camera that is connected to it. (Current 150mA, voltage 12 volts - information from the documentation) The
Screen has constant power, the camera only when the transmission is turned on.
All this was put on the car when the engine was not running, everything showed clearly, as it should.
It was worth starting the car, as horizontal interference began and at the end a white screen, this is provided that the car started when the reverse gear was stuck and the camera was working.
If the camera was not initially turned on in reverse gear, then after starting the engine, the screen did not even come to life in terms of showing the video from the camera.
What could it be?
There was a finger poked into the sky suggestion that it was all because of the voltage, when the car was 11.8 volts, when it was running, 14 volts, a 12 volt regulator was installed on both power supplies, it did not help.

Answer 1

Everything is in the screen, the screen is on the case, the power supply, except for stabilization, is filtered - inductor + capacitors, or powered through a DC-DC PSU.