Tbc is trailer brake controller that can help make braking with the trailer attached smooth and effective when the tow vehicle brake pressed .It has a manual control lever that sends the independent power to the trailers brake .If manual control is activated while the brakes are also applied ,the greater of the two inputs determines the power sent to trailer. Usually the trailer brakes controller is at the centre but it varies from model and year of manufacture. On the screen you can see the power gain or loss when you’re foot is on the pedal.Braking force applied is directly proportional to the force applied to the braking pedal , depending upon gain settings.

Ford tbc fault is the problem in tbc connection in ford vehicles.There are tbc codes which appear on your dash saying tbc fault that indicates tbc faults.
If you have trailer attached to your vehicle it means you are losing your connection or ground to the trailer and if trailer is not there it means there is some problem with the brakes. So ,check your connections whether they are in good condition or are loosen ,dull or is there any other problem and visit the mechanic to get it done properly.