Brake Light Switch: Description and Operation

The brake lamp switch is located under the instrument panel, at the brake pedal arm. It has three internal switches controlling various functions of the vehicle. It's main function is to control operation of the vehicle's brake lamps. Other functions include speed control deactivation, brake sense for the antilock brake system and brake sense for the brake transmission shift interlock.

CAUTION: The switch can only be adjusted once. That is during initial installation of the switch. If the switch is not adjusted properly or has been removed for some service, a new switch must be installed and adjusted.

When the brake pedal is pressed, the plunger on the outside of the brake lamp switch extends outward. This action opens or closes the contacts of the three switches inside the brake lamp switch.

With the brake pedal pressed down (plunger extended), the switch for terminals 1 and 2 is closed completing the circuit. The switch for terminals 3 and 4 is open and so is the switch for terminals 5 and 6.

When the brake pedal is released (plunger pushed in), the three switches assume the opposite positions. The switch for terminals 1 and 2 is now open while the other two switches are now closed, completing their circuits.

A lever on the back of the switch is used to set the switch into the "adjusted" position. A non-adjusted switch will have the lever set to the diagonal position in relation to the switch housing. The plunger can be moved in and out, but the states of the internal switches will not change.

CAUTION: Never move the adjustment lever of the new brake lamp switch without it being properly installed in the vehicle first. Such action will render the switch unusable and the switch must be discarded.

Camshaft:

Once installed in the vehicle as described in the brake lamp switch installation procedure, the new switch's adjustment lever is rotated to the adjusted position as indicated. This action locks the plunger to the internal switches. Once in this position the switch is permanently adjusted (or locked) and cannot be readjusted or released even if the lever is moved back.