Find a good flashlight, and slide your driver's seat back. The switch for the brake lights is under the dash, mounted near your brake pedal assembly.
When you are not touching the brake pedal, the brake pedal assembly should be pressing on the switch. The peddle frame should leave the switch when you push the brake.
You have to find the switch, often very simple to do, sometimes they are hidden by all kinds of stuff. See if you can remove it, it needs to be tested with a continuity tester. Many hobbyist's have them and will be glad to check it for you. The switch is not expensive.