Camera Switch - Camera justs turns off, but does not switch

Hi, I am trying to make a camera switch and have looked at every video and thread,
but I can still not do it.
My situation is that I have this code attached and I dragged in two of my cameras . The script is attached on an empty.
When I press Tab, it just says in runtime, not cutting to the other camera[display 3]

Display 2: No cameras rendering

I use this code:

using UnityEngine;
using System.Collections;

public class CameraController : MonoBehaviour {
//Define the camera
	public Camera MainCamera;
	public Camera SideCamera;

	//Called every frame
	void Update(){
		if(Input.GetKey(KeyCode.Tab)){
			MainCamera.enabled  = false;
			SideCamera.enabled  = true;
		}

	}
}

What can I do?
Thank you in advance.

I figured it out! If you switch cameras, you have to make sure that they are both on the same TARGET DISPLAY so both cameras have to be on display 2 for example.
Hope that helps.