Why does a backup camera work without the ground wire connected and is it needed?

Question

I am in the process of installing a backup camera that has the same wiring as shown in this picture:

The cable in the middle with a red and black wire coming off of it connects to one of the two cables coming from the camera on the left. The instructions state to connect the red wire to the reverse light's positive (+) wire and connect the black wire to ground.

The cable on the right has a RCA cable along with a single wire that appears orange in this photo. This is run from the rear of the car to the front of the car. The RCA cable plugs into the backup camera input on the rear of the stereo to transmit the video from the camera. The orange wire is to trigger the car stereo to display the backup camera image when the car is in reverse. The orange wire in the trunk connects to the reverse light's positive (+) wire (same as the red wire above) and in the front of the car it connects to the backup camera trigger wire on the stereo's wiring harness.

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While I was in the process of hooking this up I completed the following:

1. The RCA cable was connected from the camera to the stereo
2. The orange wire was connected to the stereo backup camera trigger wire in the front of the car.
3. The orange wire and the red wire were connected to the reverse light's positive (+) wire.

The only thing that was not connected was the ground wire. I was going to test the camera by putting the car in reverse and then touching the ground wire to bare metal, what I was surprised to find was that the camera was functional without the ground wire connected.

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I have two questions:

1. Does anyone know how it works without the ground wire connected?
   a. Is it being grounded by the RCA cable?

2. Is there any reason to connect the ground wire or is it alright to leave it disconnected?

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For reference the actual model I am installing is a eRapta ERT3 Backup Camera, but as stated the wiring is the same as the picture above.

Answer 1

The camera was, most likely well most certainly, grounded via the rca cable with the other camera earth or ground.

Don’t rely on this as it will increase “noise” or “interference”, ie the shielding on the rca cable works when both ends ie cameras are earthed or grounded.