Installing an aftermarket radio in '12 200 convertible and have a few questions if anyone can help.

I added a clip on harness but there is no (orange) Illumination wire on it, upon testing I have a 12v constant, a 12 Acc key on, but no headlight switched 12v.
When I test the back of the factory harness there is a cable in that does not go out to radio side but it tests at below 3v and is not effected by the headlight switch.
Do this car not have one or should I cut everything off and restest each bare wire from scratch?

Can I run a manual wire from some component that is (headlight switch controlled but not dimmer) on dash to the orange illum wire on my head unit, if so what component is easy to get to and do I connect to the positive or negative side of it?

Is there a location on fuse box that is headlight switched 12v? or should I add an inline fuse to tapped connections?

On reverse cam and parking brake connections, do I connect to the positive or negative side of the reverse bulb and parking brake wires?

Also on cams there is a extra power line on the extender cables and a lead labeled campow out of my head unit, can I power the dash cam with this connection and extra built in wire (I assume it grounds through a cam line) or should I just go with the pigtail connector and manual ground each with power taps?

How in the heck do I get the back seat out, I can lift and rotate it up from the rear but it feels hooked on the front, videos online for Non convertible models show it lifting from the front with clips that release but the fronts seem to be pressed on hooks. from there I can figure out the panels for read speaker replacements but the seat is stopping me.

Thanks in advance for any insight you might offer!