My brake lights work when the car is in park, but they only work sometimes when I braked. But I have to push brake pedal hard.
It sounds like you are having an issue with your brake light on/off switch. The switch is located under the dash high on the brake pedal bar. Sometimes these switches just get pushed out of place and need to be reinstalled or readjusted to make good contact. Seek the help of a qualified mechanic, such as one from YourMechanic, to help you inspect your brake lights. Sometimes when the switch comes out of place totally, the lights will stay on and drain your battery, not to mention driving with no brake lights can be dangerous.
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