MickAP shows us an effective method if you need to pass the video wire out as well as feed the power in.
However, there are (were) some with an rf link. I was looking at these a couple of years ago. I’m not sure what is on the market right now but it can make the wiring simpler.
But I eventually ended up with a bit of a cheap cop-out and hooked the rf camera into my sat nav (Garmin rf camera → Garmin Satnav) and kept the original NC headunit.
Here’s how I connected the 12V power pair through the umbilical for the rf–linked camera mounted on that third bit of plastic.