1. Blown Fuse: Check the fuse for the brake lights. If the fuse is blown, replace it with a new fuse of the same amperage.
2. Faulty Wiring: Check the wiring between the brake light switch and the brake lights. Make sure the wires are not damaged or loose. If there are any damaged or loose wires, repair or replace them.
3. Faulty Brake Light Bulbs: Check the brake light bulbs to make sure they are not burnt out. If any of the bulbs are burnt out, replace them with new bulbs.
4. Ground Connection: Make sure the ground connection between the brake light switch and the chassis of the car is clean and tight. A poor ground connection can prevent the brake lights from working properly.
If you have checked all of these items and the brake lights still do not work, there may be a problem with the brake light switch itself. You may need to replace the brake light switch with a new one.
