Why won't brake lights turn off?
Brake Lights that Won't Turn Off
Usually the cause for this issue is that the brake light switch mounting is not properly adjusted.
Occasionally, the adjustment is correct, but the switch is defective in that the contact points inside are not opening up.
The first thing I check is the adjustment [most switches screw into or out of their mounting bracket to adjust]. On most vehicles, the switch is operated by a "plunger" which is pushed into and out of the switch body by the "arm" of the brake pedal.
When the brake pedal is in the fully retracted position, it allows the plunger to be pushed out of the switch by an internal spring, thus opening the switch contacts, and cutting off the flow of electricity, turning the light off.
I "test" the brake light switch by disconnecting the wiring harness plug and unscrewing the switch from its mounting bracket. I then reconnect the wiring harness and while having a helper watch the brake lights and while holding the switch in my hand, with my thumb I "push" the plunger into the switch body.
This should turn the lights ON. Removing my thumb, allowing the internal spring to push the plunger back out of the switch body, should cause the lights to turn OFF. If this test works, then the switch is OK and should be reinstalled and its position "tweaked" until the lights stay off when the brake pedal IS NOT depressed, but turn on when the pedal IS DEPRESSED.
Another possible cause is that the brake pedal and its arm are no longer returning to the full "up," [retracted/disengaged] position. IF this situation is not too extreme then readjustment of the switch will correct the problem.
However, IF the pedal "resting position" is too far down, then that suggests there is something seriously wrong with the brake system itself, and MUST be checked out and repaired for the sake of safety.-