What makes it a little confusing on the FL chassis is how they leave it (at least on mine it was). Look for a black plug with no wires coming out of it. This is the connector if you were to hook up the brake controller to the chassis wiring already there. Now, here's the good part. If you want to use a standard controller, you'll need the pigtail to hook to the factory harness. The only place I found that pigtail was through FL and they get like $150 for it - ridiculous! I think the US Gear controller is also a very high cost (not sure, so please check it). What you can do, though, is one of two options: 1) cut the factory harness at the connector and splice in the generic pigtail to connect the controller or 2) use the black connector already on the end of the factory harness and fabricate your own pigtail. If you make your own pigtail, the folks at etrailer.com can help you with the pin out information (pretty simple), but you'll need to have the pins and tool to install them in the connector. Good luck!
2015 Legacy SR340 360RB
2014 Jeep Wrangler Unlimited Toad
Gigi, Poppy and Sadie Lady...On the road, but not full time!