Rich Rein

Hopefully you are onto something. I thought that I had done plenty of research going into this process, and had gone with the putco blade harness as my starting point (tapping into both reverse signal and power/ground from the driver's side taillight harness - using the T harness left my work entirely reversible, should it come to that). It worked most of the time (always in the garage when attempting to troubleshoot)...but still wasn't 100%. Fast forward to tonight, and I now still have what's left of the putco blade harness to pull the reverse signal from the driver's side taillight harness, sending a signal to the relay of the freshly arrived Pod Holes harness to T into the 7 pin trailering connector behind the bumper (which also has the correct 2 pin connectors to go to the auxiliary Baja lights in my ZR2 Bison rear bumper). Pod Holes was awesome to work with, selling me just the portions of their harness that I needed (without paying for anything that I didn't, and still leaving me with my goal of no damage/changes to factory harnesses, everything is entirely reversible should it come to that). Fingers crossed that this is the 100% fix that I have been looking for - I will try to report back after a few days of various scenarios (since my previous setup was only occasionally problematic). Note: going this route (AEV rear bumper brackets, Baja pod lights, Putco blade harness that I am really only using about 20% of, and Pod Holes harness that I am using 90% of - since I am triggering every time the factory reverse lights are on, versus Pod Holes' intention to manually trigger rear bumper step lights with the cargo light switch) is maybe not as efficient as I could have been...but in retrospect this leaves me checking the two biggest boxes for me: extra reverse lighting whenever the factory reverse lamps are lit, and the ability to reverse everything to factory by removing a few zip ties and unclipping a few connectors.

At the risk of sounding snobby (because I am definitely not trying to be) - a 21 Trail Boss is not a 23 ZR2 Bison (in terms of features/wiring harness complexity). I did a lot of research before going down the path that I did with my truck to add additional reverse lighting, and @Garett Rainey had posted above to this thread and messaged me privately because he believed that he had gone down the same path that I did, and was running into problems. Admittedly, I need to go out to the garage at some point and verify the constant power at the 7 pin connector for my model/year (because I distinctly remember reading at the time that that truck worked for older trucks...but not for mine - hence the tapping into the turn signal harness). My problems are nowhere near as consistent as what Garrett is running into on the same truck - my extra reverse lights always work whenever the truck is stationary (such as when unlocking the truck/opening doors), but occasionally I will notice the reverse lights not always coming on if I try to go from drive to reverse too quickly - like when driving up to my driveway, and then reversing into it (being methodical/intention about going from one to the other is never a bad thing for other parts of the truck anyway). Further admission: the ability to easily reverse the wiring changes was desirable (all of my soldering/connections were between the new lights themselves and the new T harness going between the existing turn signal sub harness and the main body harness that it used to connect directly to). Given my much more intermittent issues, I am not completely convinced that I don't need to revisit my work - though I can never replicate the issues when parked in my driveway (even when pulling on/shaking the involved wires and connectors to try to simulate what I had initially believed to possible be a loose connector or connection).

Admittedly, I never tried that...because everything that I read said that the trailer harness was not a reliable power source (given how the electronics in the newer trucks need a completed circuit - i.e., a trailer plugged into either the 4 pin or 7 pin connector on the truck (which then also runs diagnostics on those connections to warn you about one or more lighting issues on your trailer). Instead, tapping into the turn signal harness on one side ensured a power source that was always live when you needed it to be in order to power extra reverse lighting (with the bonus of extra LEDs adding minimal extra draw, at least relative to additional traditional light bulbs).

Just to follow up (in case this helps anyone else) - I used the Putco harness. The reverse power comes from the driver's side, as does 3 of the four wires for the extra 4 pin connector (the green power wire is the only one to come from the passenger's side). As I was only using the harness to power auxiliary reverse lights (which I wanted automatically tied in to my truck's reverse function, no extra switch needed), I cut off the 4 pin connector on the Putco harness (which means that I no longer needed the passenger side connection at all), and used the reverse wire and ground wire coming off of the driver's side piece of the harness (capping off the other two wires and hiding the ends in the loom). Power from my auxiliary lights connected to the white wire from the harness, ground from each light to the black wire...and I am in business. No issues, works exactly as I had hoped - and looks factory in the way that it all connects in (and easily removable without lasting effect because of the Putco harness).

@nlindste I am looking at doing something similar,and trying to visualize this all while parts are en route - does the putco harness go between the trailering plug and the body harness as well as have to tap/connect into the taillight harness? Or just behind the bumper, and then some connecting to whatever auxiliary reverse lights you are adding?