Why would brake lights be stuck on?

Answer 1

You do not mention year, make, and model of your vehicle, and this is necessary to a completely accurate answer, as on different vehicles, there are different ways of sensing the application of pressure to the brake pedal. And although there could be more than one reason, 99% of the time, when brake lights are stuck on, it is because the brake light switch is out of adjustment.The most common sensing method is a spring loaded plunger operated switch mounted on the dashboard frame, just above the arm of the brake pedal. The switch is positioned/adjusted so that when the brake pedal is in the fully retracted [brakes NOT applied] position, the switch is "open," or "off." Upon application of pressure to the brake pedal, the pedal arm moves away from the switch, allowing the spring loaded plunger to extend outward from the switch body, which allows the switch to close, thereby allowing electrical current to flow to the brake light circuit. This type of switch is both mounted, and adjusted, by a threaded nipple around the plunger, which is screwed into the threaded mounting bracket on the dashboard frame. Adjustment is accomplished by screwing the switch body into or out of the bracket, until it is positioned at the right distance from the brake pedal arm, so that the brake lights are out when there is no pressure on the brake pedal, and the lights are on when the brake pedal is depressed. Another type of sensing of application of the brakes is a hydraulic pressure switch mounted in the brake line system, usually at the brake master cylinder in the engine compartment on the forward side of the firewall. To my knowledge, there is no adjustment for this type of sensor, and if the brake lights are staying on, then it probably is going to require replacement of the switch.