Oh no! My cover is blown! Just kidding ya.

I ended up tracking circuits back to the firewall and ignoring the pigtail that has the 7 pin connector. I instead have a 6 pin connector installed that is only used with the gooseneck, and a 7 pin on a pigtail for standard trailers. The tractor is set up to operate the brake lights and turn signals on the tractor itself with the typical dual filament bulbs, much like a straight truck or pickup. The pigtail, as you are aware has the turn signals separate from the brake lights, and would require an adapter to combine the brake and turn currents. Probably could get creative with diodes and such, but more than likely you could tap into the tractor circuit near the rear tractor lights. The brake controller is wired just like the controllers in pickups, by finding the brake light switch.

The two tractors I have done are both Macks, an R model and now a CH 613, I can only assume the other brands are similar.