Trailer lights are the safety feature, and it is frustrating for drivers when these are not functioning. Many people complain that these don’t function when you turn on the headlights. These help alert the drivers about the towing vehicle.
Trailer lights not working when the headlights are On is due to debris around ground wires, corrosive ground connections, loose and poor fitting of ground wires, dirty connectors, greasy and painted ground connections, water entry inside lights, and overloaded wiring harnesses.
It is not safe to drive when trailer lights are not functioning because of the increased risk of accidents. The situation is more dangerous when driving at night and in low-light conditions because it can increase the risk of rear collisions.
| Reasons | Solutions |
| Debris near ground wires | Use a soft-bristled brush |
| Corrosive ground connections | Replace the corroded screw |
| Loose and poor fitting of ground wires | Tighten the screw of the ground wire |
| Burnt-out bulbs of trailer lights | Replace burnt-out bulbs |
| Dirty and corroded connectors | Clean the connectors with electric cleaners |
| Greasy and painted ground connections | Sand the surface |
| Water entry inside lights | Seal with silicone lubricant and rubber gasket |
| Blown out the fuse and overloaded the wiring harness | Replace the fuse and frayed wires |
Debris near ground wires
Trailers have different lights on their rear side to improve the driving experience. The safety feature alerts the drivers on the road that you are towing something with your truck, and they maintain the distance from you.
These lights include turn signals, running, reverse, and running lights. Ground wires are necessary to deal with unusual electric flow from the circuits.
These increase the longevity of electric equipment by preventing them from fluctuating current supply and power surges. Ground wires also provide an additional path for the flow of unusual current when normal circuit flow is not available.
These are white or green in your trailers, depending on their models. The positive terminal of these wires is connected to the power source, and the other terminal is connected to the trailer frame.
The different electrical component works when current passes through these wires. Sometimes the debris accumulates near these wires and affects their functioning.
Trailer lights draw extra power because of debris and dirt accumulation when you turn them on with headlights. The issue comes from the drawing of additional amperage from their wiring harnesses.
Dust and debris accumulate on the frame when you do not clean them after the trip. Moreover, driving on muddy and wet roads also causes debris to accumulate on the frame.
Keeping them clean and removing the dust from their frame is necessary. Use the soft-bristled brush to scrap off the dried mud residues and then wipe them off with a cloth.
Corrosive ground connections
Trailer lights shut off suddenly when you turn on the headlights because of corrosion in their surroundings. Ground wires are connected to the metal frame at risk of corrosion.
Corrosion issues come from rusting of the metal frame and screws. Rust comes on the metal frame and screws when these come in exposure to water, oxygen, and other elements.
Corroded ground wires do not conduct electric current and affect the functioning of lights. Power surges and fluctuating currents cause the electric bulb to burn out and blink.
The issue comes because corrosion builds the conductive material layer on the wires, making them resistant to electric current. Removing the corrosion from the metal frame is necessary so it cannot increase the resistance.
Replace the corroded screws with new ones to secure the ground wires on the frame. I use the dielectric grease spray near their surroundings to protect them from rust.
Loose and poor fitting of ground wires
Metal screws are used to connect the ground wires to the trailer frame. The loose connections of these wires lead to the malfunctioning of running, reverse, and brake lights.
These stop functioning and turn off when you turn on the headlights. The issue comes because of loosely connected ground wires and power surges.
The connections become faulty because of loose screws of ground wires. The corroded screws also lose strength and cannot hold the wires with the trailer’s frame.
The wire connection also becomes poor because of driving on uneven roads. Vibrations and jerks from these uneven surfaces cause them to come off.
It is better to replace the corroded metal screws with new ones. Reassemble the wire and tighten the screws to connect properly with the metal frame.
Burnt-out bulbs of trailer lights
Trailer lights mostly contain incandescent bulbs for illumination purposes. These are less reliable than LED bulbs and are more prone to burnout.
The durability of these bulbs is less and sudden changes in the current supply can damage them. In addition, the longevity also depends on the usage frequency.
These can burn out when you use them frequently and for a longer time. Moreover, the issue also comes because of vibration from the road.
Uneven roads cause excessive vibrations, which can break their filament. The loose and dirty connections of the ground wires and voltage spike cause this problem.
Replace the bulb with new ones and ensure their correct installation because it can cause them to burn out again.
Dirty and corroded connectors
Connectors are the main parts of the trailers, transferring the electric signals from the towing vehicle to the towed ones.
There are many types of connectors depending on the lights of the trailers. Most of them contain 4-pin to 7-pin connectors for the transfer of electricity.
It contains the plug and sockets that connect your truck’s electrical system with the towed vehicle. Dirty and corroded connectors lead to flickering, dimming, and complete failure of lights.
The connections become dirty when rain, mud, dirt, and debris accumulate on their surface. The issue comes when these are not tightly connected.
Incorrect sealing because of their wrong size leads to the accumulation of debris and corrosive elements. Turn off the engine to cut off the power supply and remove the socket from these connectors. Use the wire brush to remove dust and debris from them.
Spray the electric cleaner, leave it for a few minutes, and then wipe them with a dry cloth. Spray the silicone-based lubricant or dielectric greaser on their surface to prevent dirt and corrosion.
Greasy and painted ground connections
People often connect the ground wires to the trailer frame without cleaning them. Greasy residues are present on them because of the use of dielectric greasers on metal frames to prevent rusting.
These greasy residues make the insulated layer and cause resistance in current flow. The additional current cannot pass through them because of the insulated layer.
The painted frame surface also causes the same issue and causes resistance in electricity flow. It is better to clean the frame surface while securing ground connections.
Sand the frame surface to remove the paint coat, and then fasten the ground wire with metal screws to fix the issue with the trailer lights.
Water entry inside trailer lights
Some trailer lights are mounted on the back side to alert the vehicles coming behind you. It is necessary to turn them on so they can maintain the proper distance to reduce collision chances.
These are located on the rear bottom corner of your towed vehicle. Water splashes from the roads can come on them and enter inside.
Water splashes come on them when driving on wet roads during the rainy season. Moisture enters inside their bulb and causes them to burn out.
In addition, water can also enter inside when you store them in highly humid areas. Sealing them with silicon lubricant and rubber gaskets is better to prevent moisture entry.
You can also use dielectric grease sprays because these can repel the water from their surface.
Blown out the fuse and overloaded the wiring harness
The trailer lights stop functioning because of the blown-out fuse and broken wires. These electric components also contain a fuse to protect them from power surges.
The current cannot pass through the blown-out fuse, and you cannot turn them on. The broken wires cannot provide electricity connections to their connectors.
These do not function because of the overloading of the wiring harness that occurs when you turn on different electric items.
You can remove the blown-out fuse from the fuse box and replace them with a new one of the same amperage. Check the wiring harnesses and replace the frayed wires with new ones.
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