Using an original camera with the aftermarket head unit.
In general terms this can be done on most cars but it will need a little more work.
Before the original stereo is completely
disconnected from the car you need to work out which cable is providing the
image from the camera. In nearly all cars this cable is also carrying
power to the camera from the head unit and so whilst the cable is still
connected each wire on that loom needs to be tested. Most camera are
powered from the head unit at 6V - not 12v and so it is a matter of also
providing power to the camera.
The unit units also need a trigger from the car so they know when the car is in reverse. On cars which use CANBUS this trigger is provided already but if your car does not have CANBUS then again a multimeter will need to be used to test all the other cables to see which cable is providing the trigger signal. This wire needs to be connected to the blue wire labelled BACK or REVERSE.