Arunkumar.ss/Shutterstock The direct answer to whether it's possible to interchange the brake light and taillight bulbs will depend on the vehicle. Some vehicles have taillight designs that use a single bulb for both the brake light and the taillights, like some of these models with taillight designs ahead of their time. In that case, the bulb has dual-contact filaments, which you can see by inspecting the two wires inside the lens. One filament is for the brake circuit, and the other is for the taillights. It also means the bulb operates at two brightness levels, with the brake light being brighter than the taillight. There's no chance of interchanging the brake light and taillight in a dual-contact bulb, since only one bulb handles the two lighting duties. Other vehicles have separate bulbs for the brake lights and rear lamps. Those bulbs are most likely single contact with a single filament inside the glass housing, which makes it possible to interchange them if the setup uses the same bulbs. Then again, it depends on the type and size of the bulbs, so it's best to consult the owner's manual regarding bulb replacements. Some cars have brake lights that share bulbs with the signal lamps. As a side note, replacing an entire assembly may be necessary if, for instance, one LED bulb fails in an sealed LED taillight design. For clarity's sake, this article refers primarily to incandescent brake lights and taillights that can be swapped out or replaced if busted. Will a brake light bulb fit in the rear light housing and vice versa? Mihajlo Maricic/Getty Images If the brake and rear lights use separate bulbs, it may be possible to interchange them if the bulbs are of the same size and type. Most vehicles use 1156 (BA15S) single-filament bulbs or 1157 (BA15D) dual-contact bulbs for the taillight assembly. The 1156 bulb offers a single brightness level and has a single contact at the bottom. It's typically found in brake lights, reverse lights, turn signals, and other lighting applications that require a single contact design. The 1156 bulb is typically rated at 21 watts. On the other hand, the 1157 has dual filaments and dual contacts at the base, enabling it to function for running lights and brake lights. Most 1157 bulbs are rated at 21 watts for the brake light and 5 watts for the taillight (21/5). Some cars have BAU15S bulbs that are single contact but have a different base. Regarding interchangeability, the single or dual contact points and the alignment of the side pins at the base of the bulb matter most. For reference, a dual-contact 1157 bulb can theoretically fit into a single-contact 1156 housing, but it will only function at a single brightness level. Meanwhile, you can't make a 1156 bulb work in a 1157 housing that is designed for dual-contact applications. Another difference is the bulb pins. The 1156 and 1157 have two pins opposite each other, placed 180 degrees apart. However, the BAU15S has side pins at a 150-degree angle, making it incompatible with 1156 and 1157 housings. How long do taillight bulbs last? Aliaksandr Martsinkevich/Getty Images The lifespan of brake light and taillamp bulbs will vary, depending on factors like bulb quality, type, and usage. Apart from the headlights, the brake lights are used more than any other light in your car and can fail sooner than most. Incandescent brake lights and rear lamps can last 5 to 6 years or between 700 and 1,000 hours. Driving with busted taillights or brake lights is against the law and will likely get you a ticket. Worse, they typically stop working at ill-timed moments. Changing from the stock incandescent bulbs to LED bulbs may be a worthy upgrade. LEDs may cost many times more but can last longer, are brighter than incandescent bulbs, and are more energy efficient. It's not illegal to upgrade the brake lights, rear lights, and side markers of your vehicle to LED bulbs, but it's a different story with headlights. The NHTSA does not currently permit replaceable LED headlight bulbs. It mostly has to do with the incompatibility of LED bulb designs with reflectorized housings. Sure, LEDs are better and brighter than HID, halogen, or incandescent bulbs, but they typically require projector housings to mitigate dark spots and glare.