I just bought a "new" 1976 31ft Sovereign
and a new 2007 Ford with the towing package. You didn't say if your Suburban has the towing package; however, I was as confused as you when I looked at what I needed for my set up. You could call the help line at the company you listed or you might try Southwest Wheel Company
where I bought mine. They have free shipping and their site listed free wiring harnesses with your purchase. I got the plug-in wiring for my Ford which will make it very easy to install this controller. If your Suburban is equipped with the tow package, Southwest may have just what you need and it's free with the controller. Also the brake away switch is part of the trailer and may be on it already. It should be mounted on the tongue and be a flat black small rectangular piece. There are certainly people on the Forum smarter about towing set ups than I am, but I thought you would like the "lost soul" view point.