Originally Posted by KiwiJochen

To activate ReverseCam, pin17 needs to be connected to ground.

You can connect it to ground using various methods such as a manual switch.

If you want the reverse camera to come on automatically when selecting reverse gear, you have to switch the pin to ground through some circuit in the car.

The simplest and most convenient circuit to use is the reverse lamps. However, these have 12V when on, ie: they do not switch to ground.

How to change a 12V-when-on to a ground-when-on switching signal?

You could use a circuit built with opto-couplers, transistors, FETs, even glowing valves if you want.

But the easiest, simplest method is a relay.