Five years later, I finally got this wired up and functioning. I was hesitant due to the presence of the existing wiring and general difficulty of access.
I bought a set of pin/terminal connector removal tools.
For the under-dash BCM wiring:
There is not much room to work. I disconnected a few of the large connectors down there to gain a bit of space to reach the BCM connector (blue), then swung it over towards the brake pedal to work. I removed the existing wire (like white with pink stripe?) using pin removal tool to push on pin thru window on side; and then pushed in the new green/white stripe wire in its place.

For the PDC wiring in the engine bay, the existing pin seemed larger than the new one (And I couldnt figure out how to de-pin), so I ended up just using a posi-tap connector, though I would have preferred to just repopulate the connector with the new wire. (existing wire was tan / white stripe as was the new wire)
In AlphaOBD:
CBC Config I/O: Bed Light Switch Input Present - Pin G16
>Yes
CBC Config I/O: Bed Light Switch Input Present - Pin D6
>Yes

Edit: They are even better than I expected at night. My chmsl bed lights are pretty much worthless with the topper, but these do a pretty great job illuminating the whole bed and tailgate just by themselves
