Get a test light or volt meter and check the brake light switch. You should have 12V on one side all the time, then 12V on both sides when the brakes are applied. If you don't have 12V anywhere, check fuses- if you only have 12V on one side when the brakes are applied it is a bad switch. If you have 12V on both sides when pressed, bad bulbs.
Edit- the switch is located up above the brake pedal under the dash