Is your tail light not working on one side of your car? Perhaps, this occurred recently when either your left or right tail light stopped working—brake light, signal, and reverse light.
Or sometimes, either the brake light, signal or reverse light of that tail is still working. It could be or not be a bulb problem, but this maintenance publication covers every possible cause to look for in your car.
Some of these causes can actually be fixed yourself, saving you the cost of contacting a professional mechanic. However, what you do not want to do is cross the line or not involve a mechanic when you get stuck figuring out the problem.
Tail light not working on one side: causes and fixes
If one side of your tail light won’t work or only the brake light, signal or reverse light is working on that side, consider the following:
Bad bulb
Well, you probably figured out that the bulb is not the problem but sometimes bulb looks can be deceiving. As such, you want to be a little thorough with the bulb inspection to be sure it is not the reason the taillight won’t work on one side.
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The bulbs can still be faulty even if the filament is good though.
How to fix
The easy fix for this problem without contacting a mechanic is to swap the left taillight bulb with the right taillight bulb. If the left or the right side now works but the left or right that worked before no longer works, then the problem is the bulb.
Another alternative is to install a good bulb from the working side of the tail light in the socket that does not work. Otherwise, have them replaced if they won’t work.
Faulty bulb sockets
The bulb sockets could be faulty if the tail light is not working on it one side of the car. You want to check the bulb sockets for voltage using a voltmeter.
Your ground wires could be solid Black. You may have to remove the green cap wire from the wiring to trace the wire back to where it is plugged into the harness.
There is typically a short along the circuit for a turn signal of the tail light, which may contain the tail light bulbs on the same circuit. It could then mean that the socket for either the turn signal, brake light, or reverse is burned.
How to fix
The simple fix is for you to replace the socket for the affected tail light signal. If none of the tail lights work at all, you may have to replace the entire sockets. Sockets are not expensive though.
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Ground wire problem
This could be a ground wire problem. If the ground wire is faulty, contacting a professional mechanic may be necessary to carefully inspect the affected area.
How to fix
Consider inspecting the back of the frame rail for this problem. You may be fortunate to detect the ground wire without needing the mechanic by starting here.
Dead fuse
The fuse is an electrical safety component containing a wire that breaks or melts in the event of an excessively high current. This component keeps voltage spikes or wiring from damaging electrical parts.
If the fuse is blown, the tail light will stop working on one side.
Checking the fuse
Inspect the fuse and measure the voltage across the fuse terminals via the fuse panel. You should get about 12 V with the lights on, with a good tail light connection.
When the fuse is out, try to measure the resistance (Ohms, Ω) between the fuse load side and the ground. The fuse load side is the side not showing 12 V when you remove the fuse.
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You should only get resistance if the tail light bulb is good and you installed it. If you are not certain about the bulb, just run a light terminal to ground a test like that. You should get a resistance close to 0.
How to fix
If the fuse is blown, get a replacement fuse. Make sure to replace the fuse with one that is exactly the same.
Faulty brake light switch
If the brake light on one side of the tail light is not working when you match the brakes, the brake light switch could be faulty.
The brake light switch is the little thing mounted on the back of the brake pedal and could be faulty, keeping the brake light on side of the tail light from working.
How to fix
The fix is to pull out and clean the brake light switch contacts. Replace the switch and the brake light should be back on the dead side of the tail light.
If the light comes on just slightly, add a little bit of dielectric grease and replace it again. The brake lights should now come on that tail light.
Dirty pin connector
A dirty pin connector in the modular plug for the light housings can be the reason for the tail light not working on one side.
Normally, swapping them from side to side a few times will clean them well enough to complete the circuit.
How to fix
Put electrical contact grease in the pin connector to prevent poor connection. Switch the assemblies and the affected tail light should now work.
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You may even hook the voltmeter and run some switching around to find out why one side of the tail lights stopped working.
You can also slightly bend the pins on the tail light not working to touch the connectors for better contact.
Faulty foam gasket
The foam gasket on the tail light could be damaged, stopping one side of the tail lights from working.
How to fix
The solution is to inspect and fix the damaged foam gaskets on the taillight contacting the body. The foam gasket may look fine but could have let water in onto the connector pins.
Damaged wiring harness
The wiring harness is an organized set of wires, terminals, and connectors running through your car and relaying information and electric power. This component is crucial for keeping a variety of your vehicle components connected.
If the wiring harness is damaged, it can stop one side of your tail light from coming on.
How to fix
Although this is a task for a professional mechanic, see if you can remove the light assembly and check the wiring harness for voltage using a multimeter.
If your harness has no voltage, there is a problem. Otherwise, check the light assembly wires for resistance with your multimeter, making sure the bulbs are installed. If you notice resistance change in the bulbs, try again.
If that works, swap your bulbs from the working side of the tail light to test the complete circuit. If the swap does not work, contact the mechanic.
Bernard is the lead driver and force behind his Big Dog Garage Race Team. He is the General Manager and Chief Mechanic of Jay Leno’s Garage. Bernard and his crew of seven are responsible for all repairs, restoration and fabrication of Jay’s incredible automobile and motorcycle collection.
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Just want to say thank you for the info you provide it’s been accurate easy to read and understand,
Once Again
Thank You