I want to add a reversing camera and monitor to a Peugeot 207, but a tag on the wiring loom on the rear light says maximum additional current draw is 10mA. The spec for the camera is 100mA max, and monitor 300mA max, both draw the power from the reversing light 12v supply. Any advice please.
Use the rear light wiring loom to drive a relay for a fused circuit that can deliver 500mA.
Generally relays are always the way to go with these sorts of applications. They take a small current draw but can switch significant current.
Here's an example on extremelights.co.za showing a relay being used for a much higher current draw: off road lights, but the principle is exactly the same.