Yo Powell - -
I just installed the light on my '14 last week. Gotta tell ya, maybe I got spoiled with the Custom Dynamics LEDs after installing their turn signals and run/brake/turns on my Heritage, but after I installed this on the new Street Glide ... not impressed with the output. It's a little dim for what I expected. But, it does fit nice on the rack. I used the smoked lens. Looks good, actually looks great. The light output though, leaves a little to be desired.
Anyway, you're looking for where the pigtail goes. And I had the same question myself after taking off the seat and looking at the instruction diagram. The plug you want is actually the one that is mounted on the bracket (#2 as it is indicated in the diagram, if memory serves). It is the OUTSIDE plug. Following the wire towards the rear of the bike you'll see that this harness disappears behind the left side plate. To verify, just unplug it and you'll see that your rear run/brake lights are disconnected.
To attach the new pigtail provided in the kit, if you remove the existing plug you'll see it is held in place with a nylon barbed insert. That insert can be removed and re-attached to the new pigtail connector, then re-inserted where the factory plug was removed. Follow? Helps keep things tidy under the seat. And there is enough room to push the tail end of the factory harness down towards the fender without interference.
If you follow this, cool. If necessary I could post some pics.
Btw, I also ended up spending about an hour (I'm slow) trimming wire lengths and picking at the pins to get it just right. Actually a pita. Worth it though in my book.
Happy trails man