8 Reasons Why Your Brake Lights Work But Your Tail Lights Don’t
Like any other part of your car, your tail lights can also fail, creating a serious safety risk. Not only is this dangerous to other road users, but it could also result in you getting a ticket from the police or failing your state license test. But what does it mean if your brake lights work but your tail lights don’t?
Common Reasons Your Tail Lights Don’t Work But Your Brake Lights Do
1) Bad Tail Light Fuse
The first thing you should check when you encounter a fault in any electrical component, especially your lights, is the fuse. A fuse is basically a metal band in a plastic container that blows when the current flowing through it gets too high. This protects other parts of the electrical system from damage.
Typically, there are two areas in a car where fuses are located:
1. The first is the fuse box inside the car. This is usually located on the driver or passenger side, behind a plastic panel under the dashboard. In some cars, they’re located in the glove box or on the side of the dashboard when the passenger door is fully open.
2. The second area where you’ll often find fuses is the main fuse box under the hood. It’s a big black box with lots of cables connected to it. Removing the top cover gives you access to the fuses inside, such as the turn signal and headlight relays.
Once the fuse that controls the tail lights has been identified, it can be tested with a fuse tester. If the fuse is good, it will light up. If it doesn’t, it should be replaced with a fuse of the same size and rating. With certain fuses, you can visually detect a broken metal wire in the blown fuse.
2) Faulty Tail Light Bulb
If the fuses under the hood and in the cab are fine, the next culprit to look at is the tail light bulb itself. This usually requires removing the tail light cover, but some cars are equipped with an access panel where you can reach in and remove the bulb from the lens.
The filament is the wire inside the bulb that provides the light. If the filament breaks, the light won’t come on and you’ll need to replace it with a new bulb. Have you already replaced your bulb with a new one but it still won’t light up? Read on.
3) Drafting Error
In some cases, the socket into which the light bulb is inserted may be damaged. Usually, this occurs due to corrosion caused by moisture getting into the socket. However, it may also be that the wires on the back side are disconnected due to a bad connection.
If both the bulb and the fuse are fine, check the condition of the socket while removing the bulb. Check for any discoloration (white, blue, brown, etc.) and any bent or broken pins.
At this point, it’s also a good idea to check the current with a multimeter at the outlet. If you don’t get power to the pins, it means there’s a fault somewhere in the power line.
4) Worn Wiring
If there’s no power at the outlet and the fuse is working fine, it’s very likely that there’s a damaged or open circuit somewhere in the wiring.
At this point, you should get a wiring diagram and visually inspect the wiring along the tail light circuit for any breaks or torn insulation. Be sure to check the body ground from this circuit as well. A dirty, loose, or damaged ground wire can cause problems with power delivery to the outlet.
5) Control Switch Error
Another reason your tail lights won’t turn on is the switch that controls the tail lights. The headlight switch on your dashboard can also fail, so you’ll want to check if everything else is OK.
Typically, this switch turns on the headlights, taillights, and parking lights. If all other parts of the tail light circuit are working properly, this switch may be defective. You can remove it from the dash and check it with a multimeter to identify the defect.
6) Dirty or broken ambient light sensor
Many modern cars have an ambient light sensor in the dash. This allows the vehicle’s computer to automatically turn the headlights and taillights on and off depending on how bright or dark it is.
On some newer vehicles, it also turns off the daytime running lights. If your parking lights and headlights won’t work, but your brake lights do, this could be the cause.
However, this again affects both headlights and taillights, so it’s easy to test by manually turning the headlight switch to the on position.
7) Faulty Light Control Module or Body Control Module
Modern vehicles use electronic modules to control various systems, including lights. The Body Control Module (BCM) or Light Control Module (LCM) on certain cars can sometimes malfunction, causing issues with the tail lights while leaving the brake lights functional.
These modules receive input from switches and sensors, then send signals to activate the appropriate lights. If the module responsible for tail lights malfunctions, it may not send the correct signal to turn them on, even when other lights work normally.
Diagnosing a faulty control module often requires specialized diagnostic equipment. If you’ve checked all other components and can’t find the issue, the problem might lie within one of these modules. But it’s important to discount all other possible causes as control module failure is fairly rare (and not cheap).
8) Corroded or Loose Battery Terminals
While it might seem unrelated, corroded or loose battery terminals can cause various electrical issues, including problems with tail lights. The battery provides power to all electrical systems in your vehicle, and poor connections can lead to inconsistent power delivery.
Corrosion on battery terminals looks like a white, blue, or greenish powdery substance. This buildup can prevent proper electrical flow. Similarly, if the terminals are loose, they may not maintain consistent contact, leading to intermittent electrical problems.
Check your battery terminals for any signs of corrosion or looseness. If you find corrosion, clean the terminals (follow our directions). Make sure the connections are tight, but be careful not to overtighten them.