Basically the converter turns 5 wires into 4 which the trailer uses.
From the Truck….ground, left turn, right turn, running, & stop
To the Trailer……ground left turn/stop, right turn/stop, & running
The converter separates the truck from the trailer, so it’s after it “T’s” from the truck to the trailer.
This can be done a couple different ways. One is the converter box mounted under the truck box. Five in, Four out to the vehicles Trailer Receptacle.
Some use a molded-in converter directly at the vehicle Trailer Receptacle. So five wires in and four trailer connector prongs on the end. This means a big honkin plastic thing hanging on the back of the truck. Not the most desirable in my opinion.
Both, of the above, place the vehicles trailer lead in harms way when not towing a trailer. You see it driving down the road all the time. The plug flapping in the breeze, getting salt, dirt, and crud pounded on it, and then we wonder why it doesn’t work.
On my Toyota, I bought a separate converter (5 in/4out), made my own splices (soldier with liquid electrical tape) to the vehicles lighting circuits, and then ran to a RV Style 7 way Vehicle Receptacle mount directly, solid, to my hitch. (my hitch had a hole to mount in) That way the vehicle receptacle has the “flapper” to keep the crud out and no wires are dangling in the breeze when I’m not towing. This system requires a 7way to 4flat adapter to plug in the sled or boat trailer. Or you can get the kind with the 4flat along size the 7way as stated above. I had to replace mine once in twelve years because I broke it, not because it failed due to corrosion.
I’m surprised that the Frontier doesn’t already have factory trailer wiring. If it came with a hitch, it more than likely has trailer wiring. You may want to dig around, under there, and see if some wires are tape up someplace. If you find a white, yellow, brown, and a green, you should be golden! Just wire those to the 4 flat (or solid mount 7 way) and all should be good. The converter is already there in a place that no human eye has seen since the date of mfg. Heck, you might even find a blue & black one too. The blue is for electric brakes and the black is a hot charging circuit. (which you don’t need right now, but if you use a 7way, wire them up too for future reference)
Sure aint like wiring up the 72 Ford!