The brake light switch is either stuck or out of adjustment. Adjust or replace if necessary. It is located on or near the brake pedal swing arm.
Answermore likely, your brake fluid is low.
Are you talking about the "brake" light on the dashboard.. or the brake lights on the back of the car?? First, if it's the dashboard light, you need to add brake fluid or possibly change the front brake pads since the fluid runs low when the brake pads run low. Secondly, if you are talking about the rear brake lights, it could be because the little rubber pad that depresses the brakelight switch on the brake pedal when you let your foot off is worn out (has a hole in it) and the plunger on the switch is poking through the pad (which is mounted on the pedal). I fixed this problem once by simply gluing/taping a dime on the pad which made a hard surface for the switch plunger to depress against. Just look under the dash at the brake pedal and you'll see what I mean.
lost the spring for brake pad
Either, the rear bearing is dead or you need to change the brake shoes.
Check if emergency brake is fully disengaged.
If the light is on your dashboard it would be the Anti-lock Brake System
The voltage regulator inside the alternator will malfunction. Often, all the warning lights will come on: brake/batt/etc. Replace alternator.
Have you checked the fuses or bulbs?
the plug behind the battery might be unplugged or that same plug is disconnected from the fuse box
Brake bulbs. You might need to replace them. It just happened to mine and it was tricky to do it. To take the brake lights you need to pull them from the sides, there is a small piece that would come out easily and then you can just take the screws out.
A dashboard light appearing when brake pedal is depressed usually means brake fluid is low.
Check the tail light bulbs. These bulbs do double duty. Thet are both the tail light & the brake light. Tail light part might be burnt out.
you may have your brake light socket and your back up light socket in the wrong holes. Or you have a short but that would probably leave you with a blown fuse and no lights.
Two most probable possibilities immediately come to mind. To be checked out and eliminated first is that the brake light switch is not adjusted properly. The second would be that the brake light switch has become defective.j3h. check to see that brake pedal is releasing properly and not resting on brake light switch