If your brake lights are always 'on' and do not light up upon engagement of brakes, you may have a faulty or a loosely mounted brake sensor.
The sensor is located just above brake pedal (left, driver side), plugged in face down. When the brake pedal is up, it should 'click' the sensor which in turn turns off your brake lights.
The sensor has two small hooks on each side that must be pressed to release the sensor. The hooks must be fully pressed in before sensor removal.
The trick is to use a flat head and push the switch all the way up. Do the same thing with the red plastic cover. That will allow the two hooks to be completely depressed.
Do not forget to push down on the switch if you are planning on reusing the unit.
If the pedal does not fully engage the switch, raise the switch up until full contact is possible.