As I mentioned earlier, on the Voyager system, you can disable your cameras with the menu. Just hit MENU-INPUT then you scroll down to the camera that you want to disable. Once you find that camera, which will probably be cameras 2&3, then you just change the MIRROR setting to SKIP.
If you don't want to disable them completely, you can pick SPLIT SCREEN and have the benefits of both your side camera and rear camera on the monitor at the same time when you use the turn signals.
IF you do not want to go through the MENU way of doing this, the Voyager monitor pops right out of the dash without any tools. Then all you need to do is unplug the cables coming in to the back of the monitor labeled cameras 2&3. Snap the monitor back in the dash and you are good to go. If you disconnect the cameras, I would tape them off so that the next owner can decide if he wants them or not.