Your car’s lighting system might look straightforward, but when things go wrong, you’ll realize it’s far from the truth.
Take the case of tail lights. You might be confused as to why your tail lights aren’t working, but your brake lights are.
After all, don’t they light up from the same component?
Don’t worry!
We’ll help you unravel the mystery surrounding your tail lights with a step-by-step guide to identifying the issue. We’ll also provide an estimate for repairing the tail light assembly.
This Article Contains:
- Tail Lights Not Working, But Brake Lights Are: A Step-By-Step Diagnosis
- How Much Does It Cost to Fix a Tail Light?
- Can I Drive With a Broken Tail Light But a Functioning Brake Light?
- Why Is My Brake Light Not Working?
Tail Lights Not Working, But Brake Lights Are: A Step-By-Step Diagnosis
Your tail light might not function properly for several reasons, ranging from a damaged bulb to a broken electrical component. To diagnose the problem, a mechanic will inspect each suspected part individually to narrow down the cause of the faulty tail light.
Here are the steps they’ll follow to figure out why your running tail lights aren’t working but your brake lights are:
Step 1: Search for a Blown Fuse
A fuse keeps the car’s electrical system safe by acting as a protective barrier against power overloads. However, a surge from the battery or alternator can damage or burn a fuse.
Here’s how they’ll determine if a blown fuse is the culprit:
- Access the fuse box (fuse panel) under the car’s hood or behind the plastic panel near the dashboard on the passenger side (depending on the vehicle.)
- Consult the vehicle manual to identify the location of the tail light fuse.
- Remove the fuse by using a fuse puller.
- Check if the fuse is blackened or distorted in shape. Replace it with a new fuse if it’s damaged.
- If it looks fine, use a circuit test light to see if it lights up. Replace the fuse if the test light doesn’t work.
No problems with the fuse panel?
Your mechanic should focus their attention on the LED bulb.
Step 2: Inspect the Bulb Filament
Your car’s rear light bulb might have burnt out over time.
But how is the brake light still working?
In most cases, the LED bulb has two filaments: one for the brake light and turn signal, and the other for the tail light.
The mechanic will have to check if the tail light filament is broken or burnt. Here’s how they know if you need a new bulb:
- Depending on the vehicle, unscrew the tail light assembly using a screwdriver or open the trunk to access the lights from inside.
- Take the light out of the bulb socket and see if the filament wire is intact.
- Tap the light bulb against the hand to check if the filament is vibrating.
- Replace with a new bulb if the filament is broken or loose.
- If the filament seems okay, use a test light on one end of it and see if the tester lights up.
- Replace with a new bulb if the test light doesn’t work.
If the light isn’t damaged, the mechanic will need to check the attached bulb socket.
Step 3: Examine the Bulb Socket
A tail light socket can corrode due to moisture or overheat due to poor electrical connections.
Here’s how they would go about inspecting and replacing the socket:
- Turn off the light switch and remove the bulb.
- Clean the contacts and scrape off any corrosion with a screwdriver.
- Turn on the light switch and ground the tester to a screw on the car.
- Probe contacts of the socket to see if the tester lights up.
- If two of the contacts light up, insert the bulb to see if it works.
- Replace the socket if the bulbs don’t light up.
- If only one or no contact lights up, push the tester point and make contact with the wire.
- Test the wires to see if two of them light up the tester.
- Replace the socket if the wires light up the tester.
If the sockets are still in good shape, the reason for the faulty tail light may be lurking in the wiring system.
Step 4: Check for Worn-Out Wiring
This is the trickiest part of the process.
But why?
The wires run across the entire vehicle, making it difficult to locate the broken wire.
Here’s how a mechanic will fix a wiring issue:
- Consult the wiring diagram and remove the panel at the driver’s footwell near the brake pedal or tail light housing (depending on the vehicle).
- Look for a wire with a melted protective coating or a bare metal wire.
- Patch or replace the section of the wire.
- If the broken wire is in a hard-to-reach spot, remove the panels surrounding it and replace it.
Note: In case your vehicle has a trailer harness that supplies power to the trailer, a mechanic will use the wiring diagram to check the wiring around the converter (located above the left wheel well). If it’s faulty, they will remove and replace it to ensure the trailer light is working properly.
If the mechanic doesn’t find a broken wire or wiring issue even after a thorough inspection, they would need to head over to the dashboard.
Step 5: Identify If the Control Switch Is Working Correctly
Your vehicle’s rear tail lights, signal lights, marker lights, and license plate light are controlled by the same switch assembly that controls the headlights.
Like all switches, the contact leads of the headlight switch can wear out over time, preventing the running tail lights and marker lights from turning on. However, this doesn’t affect the brake light, which is connected to the brake pedal with a separate brake light switch (brake pedal switch).
Here’s what a mechanic does to access and test the headlight switch:
- Open the control switch for the headlights on the dashboard or under the steering wheel (depending on the vehicle).
- Test the contact leads with a multimeter and check the voltage reading for 12V.
- Change the control switch if there is no voltage reading or the multimeter displays ‘OL.’
Should the tail light assembly not work at this stage, the problem lies deeper in the electrical circuit.
Step 6: Test the Tail Light Relay
A tail light relay is an electrical component that controls the supply of power to the rear tail lights. Essentially, the relay acts as an intermediary switch between the power source and tail lights, ensuring the electrical current flows to them.
An early symptom of a damaged tail light relay is the tail light fuse failing more than twice. This indicates that too much current is flowing into the fuse, which means there is likely a short circuit in the tail light relay.
Here’s how they’ll confirm if the relay is faulty:
- Take apart the lower dash area and drop the fuse box to access the relay.
- Remove the relay carefully.
- Set the multimeter to measure the resistance.
- Put the probes between pins 85 and 86.
- If the measurement is not between 50 and 120 ohms, replace the relay.
- If the measurement is between the limit, continue the process by putting probes between pins 87 and 30.
- If there is a reading for resistance between these pins, replace the relay.
At this point, your mechanic would have discovered the reason behind the malfunctioning tail light or rear marker light. Based on the diagnosis, they’ll suggest suitable repairs or replacements.
Let’s take a look at price estimates for all possible scenarios.
How Much Does It Cost To Fix a Tail Light?
Fixing a tail light can cost up to $300.
However, it can be far lower depending on the cause of failure. Here are the estimates for fixing or replacing different parts (including labor):
- LED bulb: $50 – $200
- Bulb socket: $55 – $155
- Fuse: $110 – $140
- Headlight switch: $150
- Wiring system: $100 – $300 for rewiring
- Tail light relay: $100 – $115
Even though tail lights are generally not very expensive, they can still add up to a significant cost.
You might still be wondering if it’s truly necessary to fix them. Let’s find out.
Can I Drive With a Broken Tail Light But a Functioning Brake Light?
It’s not advisable to drive with a bad tail light or rear marker light, as it’s illegal, and you may end up being fined.
It also puts you and other drivers at serious risk. Even though other drivers can see you braking, they won’t be able to see the bumper and signal lights for most of your journey.
However, there are instances when your brake light and turn signal (if they share the same filament) might fail along with your tail lights. Let’s find out the cause of the brake light issue.
Why Is My Brake Light Not Working?
A brake light issue can occur simultaneously with a faulty tail light.
Here are some reasons why your brake light might not be working properly:
- Blown-out brake light bulb (commonly found in older vehicles)
- Blown fuse or damaged fuse box
- Broken brake light switch (brake pedal switch)
- Bad electrical ground due to a loose wire, corrosion, or damaged wire ends
Call a mechanic to identify the exact reason behind a damaged marker light or brake light issue.
Get Your Tail Lights Checked By AutoNation Mobile Service
Understanding why your rear tail lights aren’t working but your brake lights are can be difficult and would require expert advice.
Don’t want to risk driving to a repair shop with a broken tail light?
Let the professionals from AutoNation Mobile Service come to your driveway instead.
We’re a mobile auto repair and maintenance service that offers upfront pricing and a 12-month, 12,000-mile repair warranty.
Our mechanics can also diagnose and fix all problems with your lighting system, such as a broken reverse light, parking light, running light, turn signal light, headlight, and dash lights.
Get in touch today for any car repair or maintenance services.