What causes dim tail lights? This question arises when you notice that the tail lights aren’t working like they’re supposed to.

Instead of the normal, clear shine for every signalization light you give, you get a dim light. Often, it’s accompanied with all the lights working at once but neither one working properly.

In this article, we’ll show you some most common reasons why this happens as well as some solutions to the problem.

If you’re not in the mood for reading, you have a video at the end of the article or you can watch it on our YouTube channel.






  • Symptoms

A bad ground connection is perhaps one of the most common reasons for dim tail lights.

You’ll know that this is the problem if you see a light show coming from the tail light instead of the usual clear and distinctive signalization.

For instance, when you turn on the position and brake lights, both lights go dim at the same time.

If you additionally turn on the indicator or reverse light, it will all start working at once. One light will be brighter while the other will be dimmer. All in all, nothing will work properly.

Besides this, there is one more tell-tale sign. When you turn on the indicator and press the brake, for instance, you’ll hear, inside the passenger cabin, the turning signal sound disappearing and stopping for a moment.

  • Solution

Find the faulty ground connection and fix it.

The first place you should look is the tail light connector. Especially do this if the car is older.

Check that all the contacts are clean and rust-free. On some cars, the ground connection may have a separate wire connected directly to the car body.

Best use contact spray or WD-40 spray and sandpaper to clean the contacts. In more severe cases, you may need to change the whole connector.

If the connector is clean and OK, you should check other places down the line, especially if there are clustered ground connections in the wiring installation.

You have a separate article dedicated solely to this topic which you can read by clicking here.

Also, if you want to see how to solve problems with brake lights, click here.




  • Symptoms

All of the signalization works properly but emits less light than usual.

The reason for this may be that the bulb is on its last legs.

  • Solution

If you suspect that this is the problem, gain access to the rear of the lamp and take out the bulb holder.

When the bulb is the problem, you’ll immediately notice a black and foggy glass balloon which means lower light emission.

Replace the bulb and the problem is solved.

If you want to see in more detail how to replace tail light bulbs click here for a separate article on that topic.




  • Symptoms

Sometimes the tail lights work properly and sometimes they are dim. Also, one light might work while the other doesn’t.

  • Solution

Not only ground connections cause problems. For instance, there might be a weak contact somewhere in the positive electric input.

The solution, just like with ground connections is cleaning and tightening the electric contacts. In case of damaged wiring, best replace the wire completely.

Of course, the first place to check is the wiring connector that goes to the tail light. Other common places for problems are the contacts on the bulb holder, various other connections on the installation, and else.

Also, regarding dim tail lights, you should check the wiring inside the rubber sleeve that goes from the car body to the tailgate. This especially goes for station wagons and hatchbacks.

The bigger issue here is finding the exact location of the problem, especially with a broken wire. It can prove to be a painstaking job, often without results.




  • Symptoms

You’ll notice this immediately as the tail lights don’t have their usual, from the factory look and shine. People do this mostly to get a sporty aggressive look at the rear of the car.

There are various ways taillights are tinted. The most common ways are using tinted foil or even, the old school way, by using candle smoke.

Of course, if you’ve done this yourself, then you know what causes dim tail lights. This advice is mostly for people who have bought a car with the tail lights already tinted but haven’t paid attention to it.

  • Solution

There are options of cleaning the tail light and removing the tinted foil. This all depends on what method has been used to tint the tail light. In this case, you might need to seek advice from a professional.

Oftentimes it may be done in some homemade way which causes irreversible damage to the lens. In this case, if you want to properly solve the problem, start looking for a set of new taillights.

Anyway, the solution involves taking off the tail lights which, with most cars, isn’t that much of a problem.




  • Symptoms

All of the signalization works properly but there’s no strong light and everything is dim

  • Solution

Over time, especially in older cars, filth, and dirt finds their way into the tail light. The rubber and plastic seals between the car body and tail light may give in over time, mostly due to material fatigue.

The filth mostly gathers on the inner side of the lens making it dim and foggy.

If the tail light is not damaged, the best solution is to take it off and give it a good clean with warm water and detergent. You can also use a small brush or toothbrush to better clean the lens and reach all of the parts of the lamp.

Once cleaned and dried, it should be as good as new.

But if you see that the tail light is severely damaged best replace them with new ones.




In most cases, you’ll just need some WD-40 spray or even better contact spray.

For more rusty contacts, use some sandpaper or even a small flathead screwdriver for scraping the filth off.

If you need to remove the tail light for replacement or cleaning, a standard toolset containing 8, 10, or 13 mm sockets and wrenches should do the job. Besides this, a flathead or Philips screwdriver might come in handy.

You also might need some cutting pliers and insulation tape for wiring repairs.

For diagnosing an electric problem you’ll also need a tester or a multimeter.

This is, of course, a generalized overview. Sometimes you’ll need just one of these to finish the job and sometimes you’ll need almost all of them.

Best take a look at what you exactly need for the repair before you start.

One more word of advice: search on the internet or the car manual on how to remove the bulb holder or tail light so you don’t accidentally damage it.

Make sure to take all of the safety precautions, especially if you’re going to work around the wiring.

Take out the ignition key or, even better take off the battery clamp. This is to prevent an accidental short circuit.

Depending on the car, taking out the ignition key should be enough to cut off the power coming to the tail light.

But if you want to be 100% safe, take off the battery clamp.



So, as you’ve concluded the answer to the question of what causes dim tail lights roughly sums up to this:

  • If you get the “light show” effect, check the ground connection.
  • When everything is working properly regarding the signalization but the light is dim, check the bulb and that the tail light lens is clean.
  • When the tail light is sometimes dim and occasionally stops working, check the electric contacts and wiring.
  • If the previous owner or yourself dimmed the taillights, the answer is obvious. I would recommend getting rid of this as soon as possible as most of these are not safe because they reduce the signalization visibility.

In the end, make a habit of checking the rear signalization from time to time. At least once a month would be OK.

I’m mentioning this as it can pass days if not months until you notice that something is wrong. No need to say how dangerous this is both for you and other participants in traffic.

The car signalization always has to be 100 percent in order.



Written by: Sibin Spasojevic


Former car technician, life-long car and DIY enthusiast, author for Despairrepair.com