Retaining a factory camera

Most vehicles will have a camera retention cable to them but not all

If the vehicle is a European you may need to get a RGB Convertor as many (esp VW) will not be able to be retained without this

For all Asian cars it is quite a simple 5 minute task. 
Before removing the stereo isolate which cable retains the factory camera

With the cable isolated and connected to the stereo simply use a multimeter to work out which wire(s) have either 6v or 12V on them when only in reverse.

If 6V then you will need a regulator


Then usually, but not always, the video feed is next to this.  So again with a multimeter test the wiring to look for between 300 - 1000milliamp, again only when the car is in reverse - this will be the video feed.

Now that you have the power and video feed add the RCA onto the factory cable, and repower the camera. 

The power wire may also be needed to trigger the head unit into reverse by connecting to the Back, Camera, CCD or Reverse cable