Is 3157 a brake light bulb?
Yes. The 3157 is a common automotive bulb used in many rear combination lights as a dual-filament brake and tail light bulb. In most setups, it functions as part of the brake-light circuit when braking and also as a tail light at a lower intensity.
The following article explains what the 3157 bulb is, how it functions in a typical rear lighting system, and how to identify compatibility and replacement options.
What is a 3157 bulb?
A 3157 bulb is a dual-filament automotive light designed for rear combination lamps. It typically features a bayonet-style base and two filaments: one for the tail light (lower brightness) and one for the brake/stop light (higher brightness). In many car models, the same bulb also handles a turn signal when an amber variant is used, though some vehicles use separate bulbs for turn signals.
Base and filament details
Filament configuration and base type can vary by market and vehicle; common configurations include variations of the base that fit into the tail/brake socket. When replacing, ensure the bulb matches the base type and voltage (12V is standard for most passenger cars).
Common uses and compatibility
Before you read the list, note that bulb naming and availability can differ by country and vehicle. Check your owner's manual or a cross-reference guide for the exact part number.
- Rear combination lights on many older and some modern vehicles use a 3157 for both tail and brake functions
- Some vehicles use the 3157 as the dual-filament brake/taillight bulb in the left or right rear corner
- Amber-variant versions (often labeled 3157A or 3157NA) may be used for turn signals in the same rear housing
Concluding note: if your car uses a different bulb number or a modular lighting system, you may need a dedicated turn-signal bulb or a specific LED replacement that matches the socket and electrical characteristics.
Replacing and choosing LEDs
When replacing 3157 with LEDs, ensure the LED bulb is designed for dual-filament or dual-function use, or use an appropriate LED replacement that mimics the brake and tail functions. Some LED replacements require load resistors to prevent hyper-flashing on older vehicles.
- Choose an LED with dual-diode or dual-filament configuration to replicate two-brightness levels
- Verify fitment: base type, socket (bayonet), and voltage
- Consider anti-flicker/load resistors if the vehicle does not provide proper LED load management
Concluding note: LED replacements offer energy efficiency and longer life but may affect CAN-bus signals or lighting behavior in modern vehicles if not properly matched.
Summary
In short, the 3157 is indeed a common brake-light-compatible bulb in many vehicles, typically used as a dual-filament rear-light bulb for tail and brake functions. Some variants also serve as turn-signal bulbs in the same housing. Always verify the exact bulb type for your car in the owner’s manual or a reliable cross-reference, and consider matching bulbs in pairs to maintain consistent brightness and color.
Are the brake light and signal light the same bulb?
No, a brake light and turn signal are not the same, but they can share the same bulb in many vehicles. In many cars, especially older American models, a single dual-filament bulb serves as both the tail light (low-intensity filament) and the brake light (high-intensity filament), while the turn signal (often a separate bulb or the same dual-filament bulb) flashes the amber or red light to indicate a turn. In contrast, many newer or European and Asian vehicles have separate bulbs for each function to prevent a turn signal from failing if the brake light bulb burns out.
How they work together
- Shared bulb (common): A single bulb with two filaments is used for both the tail light and brake light, or for the brake light and turn signal.
- Filament-based system:
- The tail light uses a low-intensity filament that is always on when the headlights are on.
- When you press the brake pedal, the high-intensity filament comes on, making the light brighter.
- When you activate the turn signal, the high-intensity filament flashes for that side of the car.
- Separate bulbs (newer vehicles):
- Some modern vehicles use completely separate bulbs and circuits for the tail, brake, and turn signals.
- This design is often used in European or Asian models and is considered safer because a burnt-out bulb on one function won't affect the other.
Why it matters
- Safety: If a bulb is shared, a problem with one function could cause the other to stop working.
- Regulations:
- Regulations in the USA allow manufacturers to let the same bulb function as both the brake light and the turn signal.
- In other regions like Europe, turn signals are often required to be amber, while brake lights must be red, necessitating separate bulbs.
This video explains how to wire a single bulb to function as both a brake light and turn signal: 46sWiring RescueYouTube · Apr 20, 2023
This video demonstrates how to separate the brake and turn signals on a vehicle with shared bulbs: 1mZac CookYouTube · Apr 22, 2024
This video shows the wiring connections for brake and turn signals: 59sAmerican AutowireYouTube · Dec 18, 2018
Is 3157 a brake light?
The 3157 bulb is commonly used for tail lights, brake lights, and rear turn signals, especially in trucks like the F-150. It can also function as side marker lights on some trucks.
What type of bulb is a 3157?
Incandescent
Features & Specs
| Light Type | Incandescent |
|---|---|
| Light Source Type | Incandescent |
| Light Source Wattage | 17 Watts |
| Accepted Voltage Frequency | 100 to 120 Volts and 60 Hertz |
| Control Method | Touch |
Is the tail light bulb the same as the brake light bulb?
No, the tail light bulb is not always the same as the brake light bulb, but in many modern vehicles, they use a single dual-filament bulb where one filament is for the tail light and the other, brighter filament is for the brake light. Some vehicles have separate bulbs for each function, while older vehicles may have used entirely separate bulbs.
This video demonstrates how to change the brake light and tail light bulbs: 54sFixbookYouTube · Dec 3, 2011
How to tell
- Check the bulb: In a dual-filament bulb, both the tail light and brake light functions are housed in a single bulb. The tail light is a dimmer, always-on light, while the brake light is a brighter, separate filament that illuminates only when the brake pedal is pressed.
- Consult your vehicle's manual: The most accurate way to know is to check your car's owner's manual or look up the specific bulb type for your make and model.
- Look for separate bulbs: If your vehicle has separate bulbs, you'll see one bulb for the tail light and a different one for the brake light.
Key differences
| Feature | Tail Light | Brake Light |
|---|---|---|
| Purpose | To make your vehicle visible to others at night or in low visibility conditions. | To alert drivers behind you that you are slowing down. |
| Brightness | Dimmer, constant illumination when headlights are on. | Brighter, and only turns on when the brake pedal is pressed. |
| Bulb type | Can be a single-filament bulb or one filament of a dual-filament bulb. | Can be a single-filament bulb or the brighter filament of a dual-filament bulb. |
(this||self).Wufxzb=function(c,e,f,l,k){var d=document.getElementById(c);if(d&&(d.offsetWidth!==0||d.offsetHeight!==0)){c=d.querySelector("div");var g=c.scrollWidth-c.offsetWidth,h=Math.min(e?g:0,g);c.scrollLeft=e&&(l||f)?0:h;var a=d.getElementsByTagName("g-left-button")[0],b=d.getElementsByTagName("g-right-button")[0];a&&b&&(e=RegExp("\\btHT0l\\b"),f=RegExp("\\bpQXcHc\\b"),a.className=a.className.replace(e,""),b.className=b.className.replace(e,""),h===0?a.className="pQXcHc "+a.className:(a.className=
a.className.replace(f,""),k&&c.classList.add("pA30Ne")),h===g?b.className="pQXcHc "+b.className:(b.className=b.className.replace(f,""),k&&c.classList.add("FpCCub")),setTimeout(function(){a.className+=" tHT0l";b.className+=" tHT0l"},50))}};}).call(this);(function(){var id='_KtUlac7YO9mnkdUPkMeNkAk_139';var rtl=false;var gecko=false;var edge=false;var soh=false;
(this||self).Wufxzb(id,rtl,gecko,edge,soh);})();
This video explains the difference between tail lights and brake lights: 52sKamsiparts Automotive YouTube · Feb 17, 2024
