Bizarre Rear Camera Issue

Stop me when I go into too much detail...

I'm t'shooting a Chinaseum-brand $30 license plate mounted rear camera. Yup... one of those POS things. The thing was presented to me as functional-with-a-caveat, and just one day prior everything was working as expected.

The Problem:
The Kenwood headunit automatically displays rear camera video when the car is shifted into reverse only when the trunk lid is open. When the trunk lid is closed, the headunit display goes black; iow, rear camera video cuts in and out when the trunk lid is moved up and down. This headunit has a "CAM" button to manually toggle display of the rear camera video when the car is in reverse but video displays on the screen regardless of trunk lid position!

I found the location of the problem: A broken solder splice within the black video cable at a flex point under the trunk lid. The video cable conceals three individual miniscule conductors. I delicately re-soldered each splice, applied heat shrink tubing (HST) to each splice, wrapped the bundle in HST, then put the repair where it would never again be affected by trunk lid movement.

My careful repair promptly made the problem worse.

The New Problem:
The headunit doesn't automatically display rear camera video when the car is shifted into reverse regardless of trunk lid position; however, just as before I made my repair the headunit displays rear camera video when the "CAM" button to manually toggled while the car is in reverse. I'm stumped.

I have no idea how to t'shoot this problem at this point. My limited understanding of these POS Chinaseum-brand $30 license plate mounted rear cameras is that switching is done at the headunit where 12vDC is detected via the "Reverse" conductor (within the headunit harness) that originates waaaaay back in the trunk from the reverse light.

I've checked--and re-checked--all conductors and splices.
What do I need to do?

I'd start with wiring the camera to an ignition source and double checking the reverse trigger you are feeding the Kenwood Radio.
The camera wired to ignition source will help with any turn on delay. Trunk up and down is just a side effect of previous issues; cam button on Kenwood just activates input on demand (non-related); etc...

BTW....this statement is not accurate.
"is that switching is done at the headunit where 12vDC is detected via the "Reverse" conductor (within the headunit harness) that originates waaaaay back in the trunk from the reverse light."

It all depends on the vehicle. Reverse status could be pulled from CAN dependent on the vehicle.