How a Brake Light Switch Works

Want to know how an automotive brake light switch works? The following article describes the basic operation and wiring of the switch. This switch controls when the brake lights go on and off as the brake pedal is depressed by the driver. This is achieved by the switch plunger resting against the pedal arm.

A stop light switch is designed in the opposite way of a normal switch would work because when the switch is has contact by the pedal it is off, and when pedal is in operation the switch is on. Through time and usage the contacts inside the switch become worn and can burn and short out rendering the switch non operational.

Also see: Brake lights not working
Brake Light Switch
This brake lamp switch is designed to work with two wires or up to six wires in the switch harness. These additional wires are on older cars which send signals to various additional controls in the vehicle such as the cruise control, ABS, traction control, shift lock control and BCM inputs, and even the engine starter operation.

Newer cars just have two wires that send input information to the vehicles BCM or the electronic brake control module which delivers a trigger signal to the brake light relay which in turn illuminates the brake lights. The switch or relay control the right, left and center brake lights through the exterior lighting wiring harness.

American made vehicles incorporate the blinker operation into the brake light circuit. When the turn signal switch or multi function switch is operated the brake light circuit is substituted for the turn signal circuit either right or left. European and Japanese cars have a separate light and circuit for each. 

If the switch becomes out of adjustment it can leave the brake lights on which will drain the battery down. Since the brake light switch is used many times, it is a serviceable item and will eventually need to be replaced which is usually a simple procedure. These switches are held in place by a metal clip and pin assembly which makes replacement about a 20 minute job in most cases and can be replaced with just a few basic tools.

When it comes to electrical devices such as brake light switches, OEM (original equipment manufacturer) parts will work better and last longer.

On older vehicles the cruise control will have its own switch near the brake pedal that is vacuum operated. A shift lock system assures that the brake pedal is depressed before letting the vehicle be put into gear to avoid accidental acceleration or rolling.

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