With the electric brakes you need something to energize or control the brakes. The brakes use an magnetic field to move them or apply the brake shoes to the brake drum. The brake controller is what senses that you are braking and sends an appropite signal to the brakes on the towed dolly or for that matter travel trailer.
If you add surge brakes for the dolly, you will have to add a lot of hydraulic lines, plus replace part of the tongue (hitch) with one that has a hydraulic cylinder to apply the trailer brakes when the trailer (dolly) pushes aganst the hitch ball when stopping.
Amateur Radio Operator (KE5DFR)|Full-Time! - 2012 6.7L Ford Crew Cab Dually -2013 HitchHiker Champagne 38RLRSB - Travel with one Standard Schnauzer and one small Timneh African Gray Parrot