Do you have anti lock brakes that might be it if not your rotors maybe warped
misadjusted or malfunctioning Idle Speed Control ( ISC ) motor
A leak in your brake line, or very low brake fluid, both of which are extremely dangerous and should be fixed at once.
dahil sY0..
Your brake light switch is out of adjustment. Don't know what vehicle you have but most brake light switches are located on the brake peddle lever just above the brake peddle pad.
There is a small switch just above the break peddle that controls the lights.
There might be something wrong with the brake pads. It is a good idea to get these checked out right away.
Brake pads could be worn or lack of fluid in brake funnel
just above the brake peddle
The Anti-Lock brakes pulsate so the brakes do not lock up (anti) and cause the vehicle to side out.
Warped rotors. Driving using the left foot to brake causes the rotors to heat up. Quenching the hot rotors by driving thru water will cause them to warp. The warped rotors cause the pedal to pulsate.
You may need to check your brake light switch. It is a small switch located on top of your brake peddle (up on the arm of the peddle). This switch allows the brake lights to come on whenever you push the peddle.
soft peddle feel maybe from a damaged brake master cylinder. this pressurizes the peddle, and if there is a leak in the cylinder it might feel soft or flop all the way to the floor.