Have you checked to make sure all the other brakes are working? On a lot of TTs, the brake wiring goes from one brake to the next, instead of being "starred" from a central point. A bad connection could cause brakes on the end of the string to not work. The controller would still see a resistance, so wouldn't report "brakes not connected", but all the braking would be done by the working brakes.
Measure the resistance. Nothing in your profile, and you don't say whether you have one or two axles. A single axle, you should see 2 ohms or less. Double, about 1 ohm. Short the meter cables first, and subtract that reading from the brake resistance for a more accurate measurement.
Some controllers have a diagnostic function which will show you the resistance.