Issues with my newly installed Joying Head unit

1. How to connect reverse camera? There is no BACK wire in the harness to send the signal to.
2. Fader settings in Amp does not retain previous settings. It always resets back to full mode. What to do in order for it to stick with the previous setting?
3. How to set it to stop launching radio upon boot up? I dont listen to Radio, i always use spotify.

Fixed 1 and 2:

It seems that on the harness that comes with this unit, there's no label on the BACK wire. It is basically the orange wire, had to splice and attach the signal to it.
lastly, how do I connect a universal wireless steering wheel control? The module I have says to attach gray and white wires to Key 1 and Key 2 on the wire harness but I don't see those.