Note : The DVR is for 12V. It may burn out if by 24V after long term using. This product does not support three-way camera work at the same time, only maintain up two-way camera work such as the front camera + car camera work at the same time, or front camera + rear camera work at the same time. If you install a rearview camera, select the display for the front camera + car camera mode, then when reverse gear the screen will automatically display full-screen rear view screen. Cancel the reverse gear will be automatically restored to the front camera + car camera video mode, and the reverse gear does not affect the car inside and outside simultaneously recording. Front and in car camera are easy to install, for rear camera power is required ( if not sure, consult a qualified auto electrician)