I also did the reverse/cargo diode mod, as well as the fogs/highs. I had also done the puddle lights with interior lights mod, on my '15. Some issues that I've seen over the last few years, getting the diode lead into the hole, diode installed backwards, diode plugged into the wrong hole.
If you only want the cargoes to come on in reverse (cargoes will still work by themselves), pin the diode (1N4004) the way that @bwlaqua did, stripe end in PINK26 (NOT 27, it's empty on most of them) and the other BROWN26.
Should you also want the reverse lights on with the cargoes, use a 14-gauge (solid) wire between the same two pins/wires.
I used the smallest tip jewelers phillips screwdriver or awl to "make an opening" along side of the pin in one of the corners, after fighting with them for a while.