I suggest you might find which of the legs of the fuse slot is 'current in' as opposed to 'current out'. Using a multi meter, with the neg to the chassis, you will find that one pole is active and the other is not when checking which fuse slot to use with a fuse tap. Fuse taps have an 'in' and an 'out'. If you get it wrong, the system will work but the two fuses will be in series so that if the prinmary fuse blows, the camera will fail. If you get it right, both will work and fail independently.
At least that is what I think but I am not a auto electrician.