Brake lights on constantly

Hi I am having a frustrating problem with my Mazda 3. The brake lights stay on constantly when there is power to the battery. But when I pull the room fuse from under the bonnet they work as normal, however doing this stops anything from working on the inside of the car. I have changed the sensor on the wheel bearings/hubs, I have replaced the brake switch under the pedals. Replaced all the fuses both outside and inside, replaced the brake lights completely. What could this be? I am totally baffled

My car has 120000 miles.
My car has a manual transmission.

Experienced mechanics share their insights in answering this question :
Hi there:

It’s quite possible that you have a faulty electrical relay from the fuse box to the brake lights that is supplying power to illuminate the light at all times. It’s also possible that a brake sensor on top of the pedal is stuck in the open position due to a faulty ground. The best advice I can offer is to have a professional mobile mechanic come to your location and complete an electrical problems inspection; so they can help you pinpoint the source of this issue and recommend the right repairs be completed.

How to Identify and Fix Common car Problems ?

Our sources include academic articles, blog posts, and personal essays from experienced mechanics :

If the brake system warning light remains illuminated the brake fluid may be low or there could be a problem with the brake system. Park the vehicle in a safe place immediately and contact an Authorized Mazda Dealer. Refer to Inspecting Brake/Clutch Fluid Level (Search).
The most common cause your brake lights stay on is because of a faulty brake light switch or sensor. It can also be caused by a faulty brake pedal or a malfunction in the electrical system. If you recently replaced the rear light bulbs when it occurred, you may have installed the wrong light bulbs.
Driving with the brake system warning light illuminated is dangerous. It indicates that your brakes may not work at all or that they could completely fail at any time. If this light remains illuminated, after checking that the parking brake is fully released, have the brakes inspected immediately.
If the tail lights are illuminated even after you have used the on-off switch to command them off, that means the switch supplying power is fused shut and/or the circuit is being powered when it is not supposed to be due to a wiring fault.
Bad Switch: One common reason for the Parking Brake light to stay on is a failing or failed switch. This can be checked easily by jiggling the handle after it is down. If the light turns off (or turns off and then back on), the switch is the most likely culprit and will need to be replaced.
If one or more of your brake lights aren`t working properly, it could mean one of three things: The brake light system fuse is blown, the brake light bulbs are burned out or the brake light wiring switch is broken. All these issues are easy to troubleshoot.
Driving with the Brake Warning Light on should not be done as this is dangerous. It means your brakes are not working properly and need to be repaired as soon as possible.
Like all fuses, the brake light system fuse can be found in the power distribution center, which is under the dashboard or tucked away underneath the hood.
The handbrake warning light illuminates when you have the handbrake on. Don`t start driving until this light is off – you may have left the handbrake on slightly, and that means the brake shoes could be rubbing and they will overheat.
Another system that experiences failures that causes illuminated CEL is the brake system. Everything from low fluid levels in the lines to unevenly worn brake pads can cause this light to illuminate.
A bad brake light fuse may have resulted in the lights being stuck on or off. There may be more than one fuse for your brake lights. If that is the case, you will need to check each of them.
The tail lights, brake lights and turn signals are used most frequently. The purpose of reversing lights is to indicate that a vehicle is moving backwards and rear fog lights provide a safety function when visibility is down to below 50 metres.
A red light that flashes on and off could signal low/almost empty brake fluid, but also a serious issue with the brake`s hydraulic system. If the light comes on and stays on, you could end up with a potentially catastrophic (and costly) brake failure.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

When I put my foot on the brake my back left brake light goes off, when I take it off the brake the brake light comes on
ANSWER : I would suggest trying to disconnect and reconnect the wiring to the rear lights. I have seen these older Toyota vehicles rear lighting short out on the lights themselves due to the way the light circuit was made on the lamp housing. Look at the housing circuit on the light to see if one is touching another, and that could tell you why it is malfunctioning. There could also be a problem with the brake light switch. If you are not comfortable dealing with wires, I recommend getting in touch with a certified mechanic who can look at your brake light issue for you to see what’s going on.

Read Full Q/A … : Brake lights on constantly

EPC light on 2004 Jetta. Code said brake switch faulty, but brakes lights worked. Replaced brake switch, now no brake lights.
ANSWER : Hi there. The first thing that pops in my mind beyond of what you have listed is perhaps the electrical harness attached to the brake switch. Perhaps the harness itself is damaged or you have an exposed wire, loose ground wire somewhere. You might want to have a professional mobile mechanic come to your location and complete a brake lights not working inspection to help you diagnose this issue.

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Brake lights are not working. replaced brake light swtch still no brake lights. the third brake light the connection was melted at
ANSWER : The first thing to do is to repair third brake light and replace the brake light fuse and then see if the third brake lights work and the lower lights start working? If only the 3rd brake light starts working then you may need a further checks on the turn signal flasher or switch could be bad.

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No dash lights, back right tail light is out, no parking lights. Brake lights work though as does head lights.
ANSWER : Hi there. In many cases, when you have electrical problems like you’re describing, it’s caused by multiple electrical component failure. It’s likely that a few electrical relays are not working; especially if you have systems that utilize the same components (such as your brake light and tail lights). I would recommend having a professional mobile mechanic come to your location to complete an electrical problems inspection first, so they can pinpoint what is damaged and recommend the right repairs.

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Abs light, emergency brake light, steering wheel assist light, engine light, EPC light, traction control light
ANSWER : Hello, thank you for writing in. The vehicle does utilize a lot of the same sensors for these systems. Are there any other codes that are coming up when this code appears? If so you will want to take these into consideration when processing the repair and making a diagnosis. The module may be bad, and replacing it should fix the problem. The lights should turn off once the main computer recognizes the new module and the sensors sync up. If you believe the sensors need to be cleaned you may do so. Do as minimal as possible to make sure you are not damaging the sensor or disrupting the wiring inside. A bad connection would make the lights stay on. With so many lights that are effected by the module being illuminated, the module is likely bad or does not have a connection. Check the connection first and then resort to replacing the unit. For more help with these electrical tests, contact our service department.

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I replaced the brake light switch. Gear lever unlocked because it had locked. Now the brakes feel hard.
ANSWER : Hi, thanks for writing in. You need to check the brake switch install adjustment. You may have the switch adjusted too tight and it is holding the the brake pedal partly down. This will cause the brake master cylinder to not release the brakes when you let off the pedal. Readjust the switch away from the pedal until you feel some free play again in the pedal. This should fix the problem. If you would like help, consider having an expert automotive technician from YourMechanic come to your home or office to inspect and diagnose this issue for you, and make or suggest any repairs as needed.

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I have no brake lights and third brake light I have checked all fuses and brake pedal switch and the switch is fine and I’m still
ANSWER : Hi there. Well, you’ve listed most of the usual suspects including the brake switch, fuses and tail light assembly. However, one item you might want to also check is the accessory electrical relay. In some cases, the relay that supplies power from the brake switch to the tail light assembly will cause the issues you are describing. I always recommend that home mechanics purchase a service and repair manual for their vehicle to have a schematic accessibly, so it might benefit you to purchase one online to locate this relay or feel free to have one of our mobile mechanic some to your location and complete a brake light inspection, so they can help trace this issue for you.

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Brake sensor is to sensitive causing brakes to flicker while driving. 2005 Mercury Montego
ANSWER : Hi there – your brake light switch needs a minor adjustment. It is adjusted too "tight" or close to the brake pedal lever, or possibly has failed. Adjusting/replacing it will eliminate this flickering problem. I recommend a brake light isn’t working inspection performed by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, and give you an accurate assessment of damage and cost estimate for repairs.

Read Full Q/A … : Brake lights on constantly