I found the info here:
https://www.newtis.info/tisv2/a/en/f...ersing-lights/
This is a view looking at the passenger side of the trunk with the carpet pulled down or removed. We are interested in the black box A174, in particular connectors A174*12B and/or A174*14B. Both connectors have the reversing wire we need to tap.
Here's what it actually looks like. The two connectors are circled.
And here is the wiring diagram showing that we want the grey wire with the blue stripe out of either of the two connectors. Your choice. I went with the lower one because there was more wire to work with to make the tap.
I made the tap and then verified with a multi-meter. I got around 12.5 volts when I shifted into reverse. I then connected the wire to my Avin unit and it did trigger the unit to switch the screen and feed about 14.5 volts to the camera power wire. All's good and no need for a relay. Hope that helps.