I was wondering the same thing.
Recently, I‘ve looked into this more than I care to admit. Deciding between OEM bed lights, aftermarket, or some combo. I’ve read many comments here that the OEM lights are not very bright and others that aftermarket led strips are too bright. All subjective I guess.
To answer your question, there is a connector in the rear that should have the upstream wiring for the bed lights. With the kit you might be able to pin the connecting connector here instead of running up front; assuming terminals are the same size. You‘d have a lot of excess wire to deal with. Or if you don‘t care about wire taps / keeping totally OEM / it being reversible, you could tap the upstream wires.
Here is a description of connector and pin locations.
Maybe I missed it but I see most are tapping the cargo light in the CHMSL. I would recommend just pin into the existing circuits for the cargo bed lights in the XY670A connector near the rear of the drivers side and above the resonator? Most body harnesses have the two circuits already ran from the BCM and terminate in the XY670A connector. The harness that plugs into the xy670a connector is determined by the options installed (I.E. ram box, cargo bed light, etc). You should be able to just pin terminals 6 and 11 in xy670a for the cargo light drive (beige/white wire) and cargo light switch signal (beige/voilet wire) circuits, then ground to the nearest ground location. Easy peasy, no going into the cab to tap wires.
Additionally, you need to set CBC I/O A5 enabled to yes and CBC I/O G16 enabled to yes in the BCM configuration and the cargo bed lights will be as OEM intended in regards to wiring and function.
As an alternative to the Mopar kit, you can buy the bed Lights and required harnesses separately for roughly the same $ as the kit. This would be truly PLUG and play; no pinning/tapping required. Would still need to program. Harnesses required depends on model year and options. Attached are the part numbers needed for 2021 without Rambox, in case that’s your situation.
I ended up doing OEM lights. Bought the left light and left harness. I found the one light alone to be bright enough and went ahead and bought the right one. Made my own right harness with some spare wire and tapped into the left light wiring. They function same as OEM (light switch included) and if I ever want/need to remove, I can take out lights and put old harness back and it’s factory again.
There are tons of threads here that describe options if you don’t care about altering factory wiring or OEM functionality.