Why do the taillights suddenly turn on when the car is locked?

[DeJeffrey]

It may be due to a malfunction in the car's brake light, causing the taillights to stay on. Here is some extended information about car taillights: 1. Rear fog light and reverse light distribution: The left side has a fog light, and the right side has a reverse light, meaning it's a single fog light and a single reverse light. Turn signals and brake lights are symmetrical, with one on each side. 2. Colors: Considering the wavelength penetration of light, there are generally three colors: yellow, red, and white. For better visibility, white lights are used, such as reverse lights and license plate-related lights. Turn signals use more noticeable yellow or red colors, while lights that need to be prominent or serve as warnings include brake lights, high-mounted brake lights, nighttime lights, and width indicator lights.

[Mitchell]

I've encountered a similar situation where the taillights inexplicably stayed on after locking the car, mostly due to electrical issues. For example, the relay might be stuck and failed to cut off power, or there could be a short circuit from aged wiring—perhaps due to moisture infiltration or rodents chewing the wires. Faulty control modules are also common, where the onboard computer mistakenly thinks the vehicle is running. Additionally, a malfunctioning brake light switch could continuously trigger the taillights. When noticing this issue, I usually check the battery first because the lights can drain it, leaving you unable to start the car the next day. It's best not to take it lightly—have a reliable repair shop inspect the wiring and control unit early to prevent minor issues from becoming major hazards. I’ve fixed it myself a few times, but amateur repairs can lead to accidents, so leaving it to professionals is safer.

[Mateo]

I think it's most likely an electrical system malfunction, like a short circuit in the relay or switch. It's abnormal for the taillights to stay on when the car is locked, which could be due to the body control module receiving incorrect signals or poor circuit grounding causing leakage. Another possibility is a software bug in the vehicle, especially since modern cars rely heavily on computers—a small glitch can cause the lights to turn on randomly. Once, when I was dealing with a similar issue, I found that poorly connected aftermarket light wiring caused interference. In any case, it needs to be checked as soon as possible; otherwise, the battery might drain, affecting the next day's travel. I understand how frustrating this can be. I recommend using a multimeter to test the current flow, but if you're not familiar with electrical systems, it's best not to force it—taking it directly to a repair shop is the most hassle-free solution. If this issue isn't resolved promptly, it could also affect the functionality of other components.

[SanAxel]

The taillights turn on by themselves after locking the car. I suspect it's either a faulty switch or a short circuit in the wiring. The lights staying on drain the battery quickly, making it easy for the battery to die, and the car won't start. My friend had a similar issue, and it turned out to be rodents chewing through the wiring harness. The safest solution is to quickly disconnect the battery's negative terminal to temporarily turn off the lights. Don't delay too long to avoid accidents. Take the car to a professional repair shop as soon as possible to inspect the wiring. Don't try to fix it yourself—safety comes first.