Testing the Brake Light Switch
So, you've tested the brake light fuse and the brake light bulbs and there's still no juice flowing to those locations. In this situation, you'll want to check the brake light switch. It's a mechanism that connects and completes the brake light's circuit in the car's electrical system. It's a very basic two-wire switch: One wire controls the power going in while the other wire controls the power going out.
The switch is located near the brake pedal and it's probably marked. Once more, get out your test light and ground it as you did when you checked the fuses. Place the sensor on just one of the two wires and hold the brake pedal down as you do so. Then test the other wire. If power is connected and the switch is working properly, the test bulbs will illuminate. If it doesn't light up, the brake light switch is faulty and will need to be replaced. If your switch is a more complicated setup, consisting of more than two wires, use the owner's manual to locate the primary "power in" and "power out" wires and test those.
If you do all of these things and still can't get your brake lights to work, your car may have some different systems that need to be checked. For instance, some cars' brake lights and turn indicators are wired together, which means you'll need to inspect that combined system and its fuses. Modern cars feature a dedicated "brake light control module," along with an integrated computer system and onboard diagnostic scans to pinpoint any problems.
Fixing a vehicle's brake lights is usually an easy task, but there are occasions to consult a professional mechanic. Whatever your car requires, it's important to get those lights fixed as soon as possible.
Originally Published: Oct 18, 2010
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