According to the vehicle code in all US States, having the rear license plate efficiently illuminated at night is a requirement. This duty falls on the license plate light which is attached above the rear license plate frame and shines in a downward direction. However, since the license plate is displayed behind the vehicle you're driving, it's more likely that you won't know that a problem exists until it's too late and you've been pulled over by a police officer.
Most of today's cars, trucks and SUV's have multiple sensors, monitoring devices and computers that relay information to the driver when a potential issue exists. To our knowledge, this technology does not include the license plate light. Like the rear brake and parking lights, there are several things any car owner can do to visually inspect the license plate light before they drive at night that can save you from receiving a traffic infraction ticket.
Noted above are a few of the warning signs that an issue with your license plate light exists, so you can have the license plate light replaced by a mechanic if needed.
1. The light is flickering on and off
The license plate light is supposed to turn on when the headlights are activated including the main headlights or the parking light. The license plate light is a solid light that is either on or off. However, in many cases, the license plate light will flicker. This is commonly due to a loose wire or connection that powers the license plate light. This symptom can be very dangerous as a flickering light can be extremely distracting to other motorists on the road. It will also draw the attention of the police and most likely result in a "fix it ticket".
To avoid this, it's a good idea to complete a quick walk around once per week, before driving at night. Simply turn on the headlights, walk around to the rear of your vehicle, and make sure the license plate light is solidly illuminated. If it flickers, it's a good idea to contact a local mechanic so they can diagnose the issue and fix it as soon as possible.
2. The light seems foggy
Another indicator that a potential issue exists with the license plate light is when the light appears foggy. This is caused by condensation or water trapped inside the light's lens cap. Water can leak from the car's trunk lid into the light lens when it's cracked or has become loose. This will cause the light to appear foggy inside the license plate frame. If this situation occurs, it'll be important to replace the light lens and the light bulb, and ensure all water or condensation is removed before it causes an electrical short – which can impact other systems inside the car.
3. The light does not come on when the headlights are turned on
The most obvious signal that there is a problem with the license plate light is when the lamp is not lit when you turn the headlights on. This could either be a problem with a relay switch, a loose connection or the license plate light has burnt out and needs to be replaced. Most license plate lightbulbs are the same, but you should always check with an auto parts store or contact a professional mechanic to replace the lightbulb with the right one.
The license plate light is more important than most people would assume, as when it's illuminated, it's not a problem. When it breaks, it can lead to safety and legal problems. When you notice that the light is not working, contact a mechanic so they can replace the license plate light as soon as possible.
This article originally appeared on YourMechanic.com as Symptoms of a Bad or Failing License Plate Light and was authored by Timothy Charlet.