Every driver knows just how important brake lights or stop lamps are. Brake lights activate when you hit the brakes, effectively warning drivers behind you when you’re slowing down. This gives them enough time to react, so they don’t end up rear-ending you. As an aside, according to studies, a vehicle with an inoperative high-mount stop lamp is 40% more likely to be rear-ended.
Without working brake lights, drivers behind you won’t know when you’re slowing down, and the risk of getting into an accident is much higher. But don’t worry. Fixing your brake lights can be a piece of cake on older vehicles with a better understanding of how brake light wiring works.
How Does Brake Light Wiring Work?
Understanding your vehicle’s brake light wiring is a good place to start when diagnosing brake light issues. While the exact design can vary depending on your car’s year, make, and model, most systems are basically the same. Red light bulbs are installed in sockets that are connected to the harness. On the other end of the circuit is the brake light switch, which activates the brake light whenever you press down on the brake pedal.
The caveat is that many vehicles built since about 2002 have the brake light switch sending a signal to a lighting control module or the BCM, which then operates the brake lights, disengages the shift interlock, etc. The brake lights on older vehicles are wired in series with the brake light switch and the turn signal switch if the brake lights and turn signals share the same bulb. If the turn bulbs are different from the stop/brake lamps, the wiring will be slightly different.
How To Diagnose Inoperative Brake Lights
Here are tips on how to diagnose inoperative brake lights:
Perform a Visual Check
Ask a friend to help you operate the brake pedal while you stand outside the car and check on your brake lights. If they press down on the brakes and only one light comes on, then you’re likely dealing with a blown bulb. If both lights are out, then it’s likely an issue with the circuit.
Inspect the Fuse Block
A blown fuse can also cause your brake lights to malfunction.
Dig out your owner’s manual or the fuse panel details for your vehicle online and find the stop lamp fuse.
Some vehicles have more than one fuse panel, so it’s important that you find out which panel it is and which fuse it is in the panel. When you find it, pull the fuse and inspect it to see if it’s blown.
Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.
Pro Tip: When checking fuses, a multimeter won’t always provide good information, so use a low impedance test light, which pulls about ¼ of an amp.
Check the Sockets
If the issue isn’t the bulb or the fuse, try checking the sockets unless the stop lamps are LED assemblies as shown in the earlier illustration.
Look for any signs of dirt, corrosion, or melted plastic. They can cause your socket to malfunction, leading to brake lights that won’t turn on.
Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.
Pro Tip: Wedge-type bulbs can look just fine (no broken filaments) and still not work due to the nature of the connections on a wedge style bulb.
Check Your Brake Light Switch
If just one of your brake lights is out, it won’t be the brake light switch. If only the high mount stop lamp works but the other stop lamps don’t, it may be the multi-function (turn signal) switch or the ground for the lower stop lights.
On some vehicles, the brake light switch can get stuck after you press down on the pedal, leaving you with brake lights that won’t turn on or off. In some other cases, the brake pedal might not be making contact with the switch at all or the wires at the switch may have failed due to repeated bending as the brakes are applied. This generally happens only on vehicles like Fords where the brake light switch is mounted on the pedal instead of a bracket. A scan tool may be needed on newer cars that have a brake pedal sensor rather than a stop light switch that directly powers the lights.
If you aren’t 100% sure what’s causing the problem, ask a mechanic for help.
Check the Wiring
Faulty wiring can also cause your brake lights to malfunction. Rough and sharp metal edges chafing the wires can create short-circuits (wire touching ground) or open circuits (wire severed). Exposure to water can also cause the wires to corrode.
How To Fix Broken Brake Lights
Figuring out the culprit behind inoperative brake lights is only the first step. Now it’s time to roll up your sleeves and tackle the problem head-on. Here are tips on how to fix your broken brake lights:
Prepare the Necessary Tools
Before we get down to business, it’s best to prepare all the necessary tools first. Having all your tools at hand can make your DIY repair so much easier. You’ll likely need a test light or a multimeter. Depending on what’s causing the issue, you’ll also need replacement bulbs, wire disconnectors, or a wire stripper and the know-how to splice wires for a lasting repair that won’t cause trouble or set things on fire later on.
Use a Brake Light Wiring Diagram
Tracing all those electrical wires can be hard. Experienced mechanics can handle wire tracing, but for DIY folks, it’s all about aptitude. If you’re planning to go the DIY route, it may help to use a brake light wiring diagram. You can trace the brake light wiring, socket, and switch using the diagram, so you can better visualize the issue at hand. You can also determine whether you’re dealing with a sensor and a BCM or a hard-wired brake light switch and a turn signal switch wired in series.
Replace the Brake Light Switch
Some brake light switches are adjustable, most aren’t. If you’re working with an adjustable switch and if adjusting the switch doesn’t work, then you might need to replace it with a new one. Make sure to inspect the connector and its terminals for any signs of corrosion or damage before installing your new switch.
Replace a Brake Light Socket
Apply Dielectric Grease to the Sockets
Before installing your new sockets, use a Q-tip to clean out as much of the old grease as possible. Then, clean any remaining dirt with a wire brush, sandpaper, micro file, or electrical solvent before applying a new coat of dielectric grease.
Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.
Pro Tip: Wedge bulbs won’t have grease in the sockets, but a tiny amount of dielectric grease on the contacts isn’t a bad idea.
Can You Drive With Broken Brake Lights?
While your engine can still run even with inoperative brake lights, it’s not a risk you should take. An inoperative brake light switch can prevent the shift interlock from working right so that you might not even be able to get the transmission out of park.
Without working brake lights, you’re also at greater risk of getting rear-ended. Drivers behind you won’t know when you’re slowing down, increasing your chances of getting into an accident. For your own sake, it’s best to avoid driving until you fix your damaged brake lights. And remember to check the high-mount stop light. It’s always a good idea to fix it if it’s out even if the others are working fine.
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