Demountable camper group

Do we have an electrical guru ?
I plan to fit a wireless rear view camera , one that can be used constantly when on the move . Could I take a fused feed from the the fridge supply from the truck ( and earth ). Would the camera lose it's supply when the ignition is off or unplugged from the truck or would it pick up a back feed from the fridge ?I am guessing that it would go dead (desirable) when it loses it's earth ?

Mine is Two part as usual with us
Camera & transmitter

Receiver and screen

Camera is powered off nearest sidelight wire I could find so I can use it anytime,
transmits about 4' forward to receiver inside trucks rear light cluster then hardwired forward to screen in sun visor drivers side
camera & screen come on again with sidelights

HERE

reason its off sidelight is its switchable and handy in traffic too, where a reverse light coming on in stationary traffic might cause alarm to those waiting behind you!

I have a second camera and transmitter in headboard of truck load liner (it was a try at helping loading) it the view doesn't really help, but its powered independently and broadcasts to same receiver, the back up camera wouldn't be powered during loading remember so you don't get two views crowding the screen