Imagine driving at night and a police car flashes behind you. The officer says both your tail lights are completely dark. This common problem scares many drivers and can cost you a ticket. Good news: you can fix most cases of both tail lights not working at home with basic tools and save hundreds in repair bills.
Key takeaways: Check if only tail lights are out or brake and turn signals too. Open the trunk and look at both tail light bulbs first. Remove the bulbs and see if the thin wire inside is broken. Buy the correct 3157 or 7443 bulbs from any auto parts store. Clean the bulb sockets with sandpaper if they look green or rusty. Test the fuse marked “TAIL” or “PARK” in the fuse box under the dash or hood. Use a cheap test light or multimeter to check if power reaches the bulb sockets. Replace the headlight switch if everything else is good but still no lights.
Why Both Tail Lights Stop Working at the Same Time
When both tail lights fail together, the problem is almost never the bulbs. Two bulbs rarely burn out on the exact same day. Instead, the car shares one power source for both left and right tail lights. This design saves wiring but creates a single point where everything can fail.
Most modern cars run tail light power through the headlight switch first. Then the power travels to a fuse and finally reaches both rear lights. A bad ground connection also kills both sides because both lights share the same ground wire bolted to the car body. Water inside the tail light housing can rust the socket and block electricity on both sides too.
Older cars from the 1990s and early 2000s often suffer from melted headlight switches. The plastic inside gets hot and the contacts burn. Newer cars use a body control module that can lose the tail light signal. Trucks and SUVs sometimes have trailer wiring plugs that rust and short out the whole system.
Bad wiring happens after accidents or when mice chew wires under the car. Salt on winter roads speeds up rust on ground connections. Knowing these common causes helps you check the right parts first and avoid wasting money.
- Both tail lights share one fuse and one main power wire
- Most common causes: bad fuse, bad headlight switch, bad ground
- Bulbs rarely fail together unless the voltage was too high
- Water damage and rusty sockets affect both sides equally
Step-by-Step Bulb and Socket Check (Start Here)
Begin with the easiest and free test. Turn the headlights on and ask a friend to look at the back. Confirm only the tail lights are dark while brake lights and turn signals still work. Open the trunk or rear hatch and find the tail light access panel.
Remove the plastic or carpet cover. Twist the bulb socket counterclockwise and pull it out. Look at the bulb: a good bulb has a clean silver wire inside. A burned bulb shows a broken wire or black marks. Gently wiggle the wire with your finger; if it moves, the bulb is bad.
Pull the old bulb straight out and push a new one in. Never touch the glass with bare fingers because skin oil makes bulbs burn faster. Clean the metal contacts on the socket with fine sandpaper if you see green corrosion. Spray a little electrical contact cleaner to remove dirt.
Put everything back and test again. Many drivers discover one bulb was bad and the other looked good but was actually loose. Tight sockets make perfect contact and bring both lights back instantly.
- Always start with bulbs even when both sides are out
- Check for broken filament or black burned marks inside
- Clean rusty sockets with sandpaper and contact cleaner
- Buy two bulbs so both sides match in brightness
How to Test and Replace the Tail Light Fuse
Every car has a fuse that protects the tail lights. When too much current flows, the fuse blows and both lights go dark. Find the fuse box under the dashboard on the driver side or under the hood near the battery.
Open the cover and look at the diagram on the inside. Find the fuse labeled TAIL, PARK, or MARKER. Pull the fuse straight out with plastic tweezers or your fingers. Hold it up to light: a good fuse has a solid metal strip inside.
A blown fuse shows a broken strip or black burn marks. Replace with an exact same number amp fuse. Auto parts stores sell packs of mini fuses for a few dollars. Push the new fuse in until it clicks.
Turn the headlights on immediately. If both tail lights work, you fixed the problem in two minutes. Keep spare fuses in the glove box because road bumps can make weak fuses blow again.
- Fuse location is always shown on the fuse box cover
- Never use a higher amp fuse; it can start an electrical fire
- Blown tail light fuse often means a short in wiring or socket
- Many cars have two fuse boxes; check both locations
Checking Ground Connections Like a Professional
A bad ground is the trickiest problem because nothing looks broken is visible. Both tail lights use one or two black wires bolted to the car metal. Paint, rust, or loose bolts stop electricity from returning to the battery.
Find the ground wire behind each tail light. It is usually black and attached with a small bolt or screw. Remove the bolt and clean the metal ring terminal with sandpaper until shiny. Clean the car body metal too.
Add a little dielectric grease to stop future rust. Tighten the bolt firmly but do not strip the threads. Some cars have the main ground wire under the trunk carpet near the spare tire.
Test the lights after cleaning each ground. Many older Hondas, Toyotas and Fords come back to life just from cleaning grounds. A quick extra test: run a long wire from the battery negative to the tail light socket metal part. If lights work, you found a bad ground.
- Ground problems make lights dim or work only sometimes
- Clean both the wire ring and car body until bright metal shows
- Salt belt cars suffer bad grounds every winter
- Temporary jumper wire from battery proves ground fault fast
When the Headlight Switch Is the Real Criminal
The headlight switch carries power for tail lights in most vehicles. Plastic and metal contacts inside get hot after years of use. The tail light position burns out first while headlights still work fine.
Turn the switch to parking lights only. If front parking lights work but rear stay dark, the switch is almost certainly bad. Some cars make a burning smell when you turn the knob.
Replacement switches cost thirty to one hundred dollars depending on the model. Dashboard removal is needed on newer cars, so many owners pay a shop two hours labor. Older trucks and simple cars let you change the switch in fifteen minutes.
Watch free YouTube videos for your exact car model before starting. Buy the switch from a trusted brand because cheap ones fail again quickly. After installing the new switch, both tail lights plus dashboard lights usually become brighter than before.
- Headlight switch fails slowly; lights get dim first
- Common on GM cars from 2000-2010 and many imports
- New switch often fixes dim dashboard lights at same time
- Professional diagnosis with scan tool confirms switch fault
Advanced Diagnosis with a Test Light or Multimeter
Basic checks fix ninety percent of cases. The last ten percent need simple tools. A twelve-volt test light costs five dollars and shows power instantly. Clip the alligator end to clean metal and touch the sharp point to wires.
Turn headlights on and test the tail light socket center contact. The test light should glow bright. Now touch the side metal tabs that should be ground. The light should glow again when touching ground.
No power at the socket means the problem is before the socket: fuse, switch, or wiring. Power but no ground means bad ground wire. Both power and ground but still dark means bad socket or wiring inside the lens.
A digital multimeter gives exact voltage numbers. You should read twelve to fourteen volts at the socket with the engine running. Learning these tests makes you confident with any car electrical problem.
- Test light is fastest tool for beginners
- Always test with headlights turned on
- Write down which places have power and which do not
- Voltage drop over 0.5 volts means bad connection
Final Thoughts
Both tail lights not working is usually a simple fuse, bulb, ground, or headlight switch problem. Start with the easiest checks and work up. Most drivers fix this in under thirty minutes with basic tools. Driving with no tail lights is dangerous and illegal, so fix it the same day you notice.
| Quick Fix Guide | What to Check First | Tools Needed | Typical Cost |
|---|---|---|---|
| Blown fuse | Fuse box under dash or hood | Fingers or fuse puller | $2-5 |
| Burned bulbs | Inside tail light assembly | None | $5-15 |
| Bad ground | Black wire bolted to body | Sandpaper, 10mm socket | $0-10 |
| Rusty socket | Metal contacts in socket | Sandpaper, contact cleaner | $0-10 |
| Headlight switch | On steering column or dash | Screwdriver set | $30-100 |
| Wiring or module (rare) | Professional scan needed | Scan tool | $100+ |
Frequently Asked Questions (FAQs)
Can both tail lights burn out at exactly the same time?
No, it is extremely rare for two bulbs to burn out together unless voltage was too high from a bad alternator. When both tail lights stop working suddenly, always suspect fuse, ground, or headlight switch first. Bulbs usually fail weeks or months apart.
Is it safe to drive with both tail lights not working?
Absolutely not. Other drivers cannot see you at night or in rain. Police will pull you over immediately in almost every country. Fix the problem before driving again, even if it means buying bulbs at a gas station.
Do I need to replace both bulbs even if only one looks bad?
Yes, always replace tail light bulbs in pairs. New and old bulbs have different brightness and one will look dim. Matching bulbs also prevent you from doing the job twice when the older one fails soon.
Can water inside the tail light cause both to stop working?
Yes, cracked lenses or bad seals let water in. Water rusts sockets and can short the power to ground, killing both lights. Dry the assembly, clean rust, and seal cracks with clear silicone.
Can a bad brake light switch affect tail lights?
No.
No. Brake light switch only controls the bright brake filaments. Running tail lights use separate circuits. You can have perfect brake lights but zero tail lights, or the opposite.
Is a blown tail light fuse always black inside?
Not always. Some modern blade fuses have clear tops and the broken wire is hard to see. When in doubt, replace with a known good fuse of the same amp rating for a quick test.
Do I need a mechanic if cleaning grounds didn’t help?
Try the headlight switch and test for power first. Most remaining cases are the switch or body control module. Independent shops fix these for much less than dealership prices.
Can LED tail light bulbs cause both sides to stop working?
Yes, cheap LED bulbs without proper resistors confuse the car computer. The system thinks bulbs are burned and shuts off power to both sides. Always buy LED bulbs made for your exact car.
