Trailer Running Lights Not Working (Causes & Solution)

Are you experiencing a trailer running lights not working problem on your trailer and want to find out why and how to fix it? Worry no more because we have the answers you need.

This article provides you with the common reasons your trailer running lights are not working and how to fix this problem.

Let’s get started!

Where neither the fuse nor relay is the problem, circuit testers can be used to test the car’s side trailer connector, and this may help.

Switch on the vehicle’s headlights, then examine the pins at the back of the connector using the circuit tester.

If the light pin reflects no power, a loose or broken connection needs to be found starting from the connector to the front of the vehicle where it ends.

If, after checking everything and nothing is found to be wrong, then the problem is from the trailer. First, ensure that the connector is not dirty and has no sign of corrosion inside and outside.

All light grounds, including the major connector ground, should be connected to clean and bare corrosion-free metal surfaces.

The ground can be interrupted if there is any obstruction between the trailer frame and the light ground or if the trailer has an aluminum frame, tilt bed, or folding tongue. Connecting jumper wires to the main connector from the light ground may help.

A connector with four terminals is used to provide turn ground return, right brake, and turn, left turn, and brake signal.

A few bigger connectors, especially on bigger travel trailers, have electric brakes, reverse lights, and a 12V accessories port.

Most wiring problems encountered usually start from the connectors. The point where the light is joined to the connector could also be the problem. A loose cable joint can be another problem area.

Also Read: Brake Light Blinking (Causes & How To Fix)

How to Fix Trailer Warning Lights Not Working

How to Fix Trailer Warning Lights Not Working

How to identify and fix trailer lights can be highlighted through the following. Fortunately, most of these solutions are quick and easy. The equipment needed to carry out these repairs includes:

  • 4 in 1 screwdriver
  • Jumper cable/wire
  • Continuity tester
  • Nut cable/wire
  • Tow vehicle tester
  • Electrical contact cleaner
  • Replacement Bulb
  • 220 grit sandpaper
  • Wiring kit.

When a trailer is old, the possibility of developing a trailer running lights not working problem will be high. As a requirement for operating a trailer safely, the running light should be in proper condition and function properly.

Due to this fact, lights ought to be checked regularly. Certain problems like having a burnt bulb or damaged light ground may be easily solved. More difficult problems may also be identified and solved.

1. Troubleshoot the Trailer’s Running Lights Using a Tester

Firstly, examine the vehicle system. Make sure the tow vehicle tester is properly inserted in the trailer. If this is done, it helps the vehicle owner know if the light systems of the trailer are running properly.

Two types of connection testers exist; the vehicle’s plug configuration needs to be checked for verification. Do not rush when hooking up or joining the light harness of trailers.

Having another person is necessary as there is the need to check if the blinkers, running lights, and stoplights are working properly.

Where all lights are not as bright as expected or fail to even come on, the harness connector of the trailer at the trunk of the vehicle should be checked.

The first thing to do is remove the harness, after which a tester should be used. The light tester of the trailer, upon plugging it, will notify the vehicle owner if the issue is from the vehicle.

If that is the case, then every truck light of the vehicle should be checked to verify if they’re working as they should.

By examining everything, you can determine if the truck light has burned out or if there is a bad flasher or blown fuse.

Clean the connector if dirty, then observe if there’s a difference. Also, check for damaged or faulty wiring in the connector.

Where every light appears to work well on the tester, it is most likely that the problem is from the light of the trailer or its harness. In this case, the next troubleshooting procedure should be followed.

2. Clean the Connector Plugs

Before starting, cleaning the plug and socket with a special cleaner is advised. This should be done when the light appears dim or does not come on.

Electrical contact can be used in cleaning connector plugs, and the contacts should be properly cleaned with a wire brush.

3. Thoroughly Inspect the Trailer’s Ground Wiring

Carefully and thoroughly inspect wire connections and clean them. After doing this, ensure the ground cable is secure and tightened to the vehicle. Most running light problems emanate from issues relating to the ground wire.

Removing the ground screw of the trailer to allow you to sand the cable terminal and chassis contact properly with sandpaper. Upon inspection, if a rusty screw is found, it needs to be replaced.

Also Read: Master Warning Light (Meaning, Causes & Fix)

3. Replace Any Bad Light Bulbs

If, after following the above procedure, the problem persists, and the trailer light keeps malfunctioning, then it is most likely that a problem with the bulb exists. In simple terms, the bulbs are bad.

By a little twisting, bulbs can be removed. Make sure the newly fixed bulbs work well before fixing them. If it is just a bad bulb, then there is no need to remove every bulb. Changing that one faulty bulb is enough.

Remove the lens, fix a new bulb, and check to see if the bulb is properly fixed and working fine. Where it works as expected, then there is nothing to worry about.

4. Clean Any Corroded Sockets

Corrosion can be eliminated with sandpaper and a dowel small enough to enter tiny spaces. If the lights are still not working, the contact point and the socket may be corroded.

A 220 grit sandpaper with some hot glue and a three-eight dowel is required to clean this. The sandpaper should be attached to the end of the dowel using hot glue. This allows the sandpaper to reach places it ordinarily would not reach.

By spinning the dowel and moving it from side to side, contact points can be cleaned. After cleaning, Apply dielectric gel to contacts before fixing the bulb.

Now, the bulb ought to be working properly. Where the case is not so, and the bulb is still not working, check the mounting bolts for adequate contact between the mounting bolts and the trailer’s frame.

After inspection, if corrosion is noticed, then clean using sandpaper. Check the lights again after doing this.

5. Conduct a Continuity Test

A continuity test can be carried out to check a trailer’s wiring. This is usually done by joining connector pins and jumper wires and then connecting a continuity tester to the sockets. A bulb and a battery are what make up the continuity tester.

The bulb comes on when the circuit is working properly. Ensure continuity connection is fast and easy with alligator clips.

A break in wiring could cause a trailer running lights not working problem. To check for a break in wiring, inspect the wire connector found in front as its end links with the socket.

Attach jumper cables to connector pins using an alligator clip connected to the continuity tester.

After completing this step and the trailer running lights not working problem persists, the most likely problem is a bare or break spot exists.

Searching for the break is what should be done at this stage. Upon locating the break, the cable should be removed and replaced with a new one. Also, repair insulators by applying heat shrinkable tubing.

6. Replace the Entire Trailer Light System (Last Resort)

Do not delay in changing the entire wiring of a trailer in a situation where it looks like it is damaged.

If any of these solutions fail to solve the problem, then it is better to buy a cable harness at a good price. Lights, lenses, and a connector come with a new cable harness.

Also Read: Traction Control Light Won’t Turn Off? (Causes & How to Fix)

How to Properly Maintain a Trailer to Avoid a Trailer Running Lights Not Working Problem.

How to Properly Maintain a Trailer to Avoid a Trailer Running Lights Not Working Problem

If all the components of a trailer are properly maintained, each component’s longevity will be increased, and unexpected costs of repairing any component will be reduced.

A few precautions that may be followed to make sure the trailer is appropriately maintained include:

1. Tire Inspection

Tire checks are necessary, especially when the tire is shaky. Issues like uneven thread, swelling, and cracking ought to be checked. It is better to examine and change tire pressure when tires are not hot.

Do not release air from tires or increase pressure when the tire is hot. Damaged tires should be removed at the earliest possible chance, and the same applies to worn-out tires.

2. Cable Inspection

Every cable and cable attachment requires an inspection before using the vehicle.

3. Watch Where You Park

Make sure where a trailer is parked is flat and level ground. In a situation where the ground is not flat or leveled and the trailer tilts, ensuring a space is big enough for such tilt is paramount.

If it is parked close to a tree, look out for branches that are out of place to prevent damaging the trailer should they break off. Tires ought to be blocked before getting out of the trailer.

4. Sanitize Your Water System

The Freshwater system should be frequently sanitized. This will stop bacteria from growing and also prevents odor formation.

Water filters should be changed not less than once a year. A change is also necessary when water flow begins to get slow.

To change the water filter:

  1. Release water from the tank, and put a bucket under the tank while doing this.
  2. Unscrew all fitting above and below the cartridge.
  3. Take out the filter and replace it with another one.

5. Dump Your Tanks

When there is no intention to keep trailers for a while, it is better and advisable to dump both black and grey water tanks. When filled with less than the two-thirds required, dump them after filling them with water.

Clean the tanks, the black tanks in particular; once they are empty, make sure there is no form of solidification that can damage the effectiveness of the tanks.

Frequently Asked Questions – Trailer Running Lights Not Working

Why Do My Brake Lights Work but Not My Running Lights?

The running lights system is responsible for powering the taillights, which usually works when the key is in the “on” position. The tail light fuse comes on when the headlight is switched on. The reason brake lights function without the tail lights working is that the headlight switch is off!

Why Do All Trailer Lights Work Except Running Lights?

If no sign is found on the cable, the damage might have occurred somewhere in the vehicle. Follow the wire to the tail lights from the junction box. When the damage is found, replace that section of the wire and repair the running light system of the trailer, which should fix the problem.

Is There a Fuse for Trailer Running Lights?

Yes, there is a fuse for trailer running lights. If a trailer running lights are not working, this can be easily fixed by finding the RT or LT fuse of the trailer and replacing them if need be. This also solves brake light problems, as they both use a particular fuse.

What Can Cause Running Lights Not to Work?

If running lights do not work, observe the fuse of both lights. If a blown fuse is discovered, it must have been caused by another issue related to the electrical system, like wiring problems or a damaged socket. The ambient sensor may also be disconnected or faulty, which can also be an issue.

What Do You Do When Your Tail Lights Won’t Turn On?

This may be caused by a few bulbs burning out or going bad. However, the most likely problem is the taillight fuse burning out. To fix this, find the vehicle’s fuse box and use a multimeter or test light to check the fuse. Then, remove and inspect the fuse where neither of these tools is available.

Why Is Only One of My Running Lights Working?

If only one light does not come on, either the blinker lights or the running lights, replacing the bulb may be the easiest solution. To replace bulbs, remove the lens and fix a new bulb, then check if the problem is solved. If it does, then everything is fine.

How Do You Test the Ground on a Trailer Wiring?

Bad ground connections can be spotted in a lot of places. The trailer connector of the vehicle is one place that should be checked. Follow the white cable from the connector, and ensure it is properly tightened to the chassis or vehicle frame. Ensure that the connection is properly tightened to clean metal.

Conclusion – Trailer Running Lights Not Working

It can be very frustrating when you have a trailer running lights not working problem.

Also, driving on roads with no lights working may be against traffic regulations which may attract consequences, including paying heavy fines.

This is why it is better to carefully inspect a trailer and ensure the lights function properly. If it is observed that the lights are off, run a quick diagnosis of the possible problems and fix them before putting the trailer on the road.

The points highlighted in this article can assist in identifying specific problems and possible solutions related to running lights of a trailer. Also, trailer maintenance should not be taken for granted.

Taking trailer maintenance as something of great importance can ensure that problems like corrosion on a large scale are avoided.

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