1157 Bulb Wiring Diagram: Everything You Need to Know

When it comes to car lighting, the 1157 bulb is one of the most popular options. This type of bulb is used for both brake lights and taillights, and it’s important to understand its wiring diagram to ensure proper installation and operation. In this article, we’ll take a closer look at the 1157 bulb wiring diagram, including its components, connections, and common issues.

What is an 1157 Bulb?

Before diving into the wiring diagram, let’s first understand what an 1157 bulb is. This type of bulb is also known as a BAY15d or S8, and it consists of two filaments: a brighter one for brake lights and a dimmer one for taillights. The dimensions of the bulb are approximately 20mm in diameter and 45mm in length. The 1157 bulb is commonly used in cars, motorcycles, and trailers.

1157 Bulb Specifications

Here are the specifications of the 1157 bulb:

Parameter Value
Base Type BAY15d
Dimensions 20mm x 45mm
Wattage 8W/27W
Volts 12.8V/14V

1157 Bulb Wiring Diagram

The wiring diagram for the 1157 bulb is relatively simple, as there are only four connections:

  • Ground: This is the black wire, which connects to the negative terminal of the battery or to the metal frame of the vehicle.
  • Taillight Positive: This is the dimmer filament of the bulb, which is activated when the headlights are on. It connects to the brown wire in most cases, but it may vary depending on the vehicle’s wiring.
  • Brake Light Positive: This is the brighter filament of the bulb, which is activated when the brake pedal is pressed. It connects to the red wire, which leads to the brake light switch.
  • Turn Signal Positive: This is an optional connection, which is used if the 1157 bulb is used as a turn signal. It connects to the green or yellow wire of the turn signal switch.

1157 Bulb Wiring Diagram Example

Here is an example of an 1157 bulb wiring diagram:

1157 Bulb Wiring Diagram ExampleSource: bing.com

FAQ About 1157 Bulbs

Q: Can I use an 1157 bulb as a turn signal?

A: Yes, but you need to make sure the wiring is connected correctly. The turn signal positive wire should be connected to the green or yellow wire of the turn signal switch.

Q: How do I know if my 1157 bulb is working properly?

A: You can test the bulb by turning on the headlights and seeing if the taillights illuminate. Then, press the brake pedal and see if the brake lights illuminate brighter. If the bulb is not working, it may be burnt out or have a faulty connection.

Q: What are some common issues with 1157 bulbs?

A: Some common issues include burnt out filaments, corroded connections, and faulty sockets. It’s important to inspect the bulbs regularly and replace them if necessary.

Q: Can I replace an 1157 bulb with an LED bulb?

A: Yes, but you need to make sure the LED bulb is compatible with the vehicle’s wiring and voltage. LED bulbs may also require a resistor to prevent hyper flashing.

Q: How long do 1157 bulbs last?

A: The lifespan of an 1157 bulb can vary depending on usage and quality. On average, they can last between 500 and 1000 hours.


Understanding the wiring diagram of the 1157 bulb is crucial for proper installation and operation. By following the guidelines and tips in this article, you can ensure a safe and reliable lighting system in your vehicle. If you have any further questions or concerns, don’t hesitate to consult a professional or refer to your vehicle’s manual.