Blue Light Special in the "Things That Make you Go Hmmm" Department. Now I know why the kits aren't out there. Sometimes the way engineers do smart and dumb stuff in the same paragraph makes me scratch the skin right off my head.
In this case, they put in that very smart prewire connector for the RH blinker, then neglected to include a wire-to-wire junction to the LH taillamp for the rest of the connections. The Body Harness runs straight out a grommet to the taillamp with no intervening connector, and that complicates hell out of constructing a tee-harness that doesn't need spliced wires. It can be done, but this is about to turn into a lengthy how-to. I'm sure Nissan is working on something similar to address the screwup, but frankly it's a major
First, the problem. Here's a pic of the LH taillamp pigtail with the lamp removed. As mentioned, it's part of the Body Harness, so the only way to tee off it is to pull it inside the car grommet and all, then put a replacement grommet on the T-harness with a matching connector.
The connector is a very-standard type and the females can be found all over almost any JY Nissan, but the males are harder to find. Fortunately, there's an eBay vendor who sells pre-wired male and female shells for $10 apiece:
https://www.ebay.com/itm/Connector-Fog- ... SwjZVav732
The grommets aren't a usual Nissan type, but it's easy to make your own with "bung" or "sealing" type grommets that come without a hole. You poke your own hole, then seal both sides with Gray Death when all the wiring is done. You can get an assortment for under $15 and just pick the size that fits:
https://www.ebay.com/itm/170-Rubber-Gro ... Sw8zNeoung
Reaching the back side of the tailamp and the trailer prewire connector isn't difficult, the cargo room trim just needs to be pulled back a few inches and not removed. There's one 10mm screw, then peel up the lefthand edge of the hatch gasket. The upper and lower trim panels then just "pop" loose and the prewire connector is visible inside:
The prewire uses spade connectors of the "quick connect" or "faston" type that you can get from any parts store, you'll need one of the male type. To construct the T-harness, you'll wire one male and one female connector back-to-back and pin-for-pin to connect to the taillamp on one end and the existing taillamp connector on the other, maintaining the existing connections. Then you'll tee another wire off each one that will go to the trailer converter. Here's how it will wire. Don't forget to put the grommet on the wires before splicing them together or you'll be taking it apart again.
Happy to answer Q's if anything isn't clear, and happy trailering!