12v power for rearview camera + monitor

[azeeroth]

I bought a kit off ebay that has a rearview mirror with an LCD monitor in it, and a reversing camera. I'm trying to connect the monitor and the camera's power up to the reversing circuit so they switch on when I put the car in reverse. They both use 12v so it should be easy enough right?

Using the diagram CTscott had in another thread, I'm connecting to the red wire #22 on 4B. Which wire do I use for negative? I measured one of the black wires (#24/25ish?) with the multimeter but it only gave me .6volts with the car on and in reverse?

So assuming there's a wire there that I can use to have 12v when the car's in reverse, I'll put the monitor on that one? But the camera itself can be on 12v all the time? Or do I do it the other way around?



Thanks, I'm an electronics newbie but I'm getting there.