Trailer light problems can turn a simple journey into a frustrating and potentially dangerous situation. Whether you’re towing a boat, caravan, or work trailer around Auckland, faulty lighting not only risks a fine but also compromises your safety and that of other road users. This article covers the most common trailer light issues, how to diagnose them, and the practical steps you can take to get your lights working properly again.
Common Trailer Light Issues and How to Fix Them
No Lights Working at All
When none of your trailer lights are functioning, the problem usually lies with the connection between your vehicle and trailer. Start by checking the plug connection at the back of your towing vehicle. Dirt, corrosion, and moisture are common culprits in Auckland’s humid climate, particularly if your trailer has been near the coast or exposed to salt air. Disconnect the plug and inspect both the vehicle socket and trailer plug for any signs of green or white corrosion. Clean the contacts using a wire brush or fine sandpaper, then apply a light coating of dielectric grease to prevent future corrosion.
If the connection looks clean, the next step is to check your vehicle’s fuse box. Most vehicles have a dedicated fuse for the trailer lighting circuit, and a blown fuse will cut power to all trailer lights. Consult your vehicle’s manual to locate the correct fuse and inspect it for damage. Replace it if necessary with the correct amperage rating. It’s worth keeping spare fuses in your vehicle for situations like this.
Another possibility is a faulty earth connection. Your trailer requires a solid earth path to complete the electrical circuit, and this is often achieved through the chassis connection. Check that the earth wire from your trailer plug is securely fastened to a clean, bare metal surface on both the vehicle and trailer. Paint, rust, or loose connections can prevent proper earthing and cause total light failure.
One Side of Lights Not Working
When only the left or right side of your trailer lights fails, you’re typically dealing with a wiring issue on that specific side. Begin by checking the connections inside the trailer plug itself. Over time, vibration and movement can cause wires to work loose from their terminals. Remove the plug casing and ensure each wire is firmly connected to its correct pin. Pay special attention to the wire that corresponds to the non-functioning side.
Trace the wiring along the affected side of your trailer, looking for visible damage such as cuts, abraded insulation, or pinched wires. Wiring can get damaged where it passes through metal channels, rubs against moving parts, or gets caught on obstacles during reversing. If you find damaged sections, repair them with proper automotive-grade wire and weatherproof connectors, or replace the entire length if the damage is extensive.
The problem could also be a poor earth connection on that particular side of the trailer. Many trailers have multiple earth points, and corrosion or looseness at any of these can cause lights on one side to fail. Check all earth connections along the affected side and ensure they’re making good contact with clean metal surfaces.
Brake Lights Not Working
Brake light failure is particularly dangerous and will definitely attract unwanted attention from police around Auckland. If your trailer brake lights aren’t working but other lights are, start by testing whether your vehicle’s brake lights are functioning correctly. Have someone press the brake pedal while you check that your car’s own brake lights illuminate. If they don’t, you’ll need to address that issue first before troubleshooting the trailer.
Assuming your vehicle’s brake lights work, check the brake light wire in your trailer plug connection. This wire should carry power only when the brake pedal is pressed. Use a multimeter or test light to confirm voltage is reaching the trailer plug when the brakes are applied. If there’s no voltage, the problem lies with your vehicle’s wiring or the tow bar installation. If voltage is present at the plug but not at the trailer lights, you have a wiring fault somewhere in the trailer circuit.
Also inspect the actual brake light bulbs and their holders. Corrosion in the bulb sockets is extremely common, especially on trailers used near Auckland’s beaches or boat ramps. Remove the bulbs and clean the contacts thoroughly. Check that the bulbs themselves haven’t blown by testing them in a working socket or using a multimeter.
Indicator Lights Flashing Too Fast
Rapid indicator flashing usually indicates that one or more bulbs have failed, causing a drop in electrical load that makes your vehicle’s flasher unit operate faster. Check all indicator bulbs on both your vehicle and trailer to identify any that aren’t working. Replace blown bulbs with the correct type and wattage. Using incorrect bulbs, particularly LED replacements in a system designed for incandescent bulbs, can cause this issue.
If all bulbs are working but the flashing remains too fast, you may have a compatibility issue between your vehicle’s electronics and the trailer lighting. Modern vehicles with LED lights and sophisticated computer systems sometimes struggle with traditional trailer lighting. This can require the installation of a dedicated trailer module or load resistors to correct the flash rate and prevent error messages on your dashboard.
Dim or Flickering Lights
Dim trailer lights that flicker intermittently point toward poor electrical connections or voltage drop issues. This is one of the most frustrating problems because it can be intermittent and difficult to pinpoint. Start by checking every connection point in the system, from the vehicle’s tow bar wiring through to each individual light. Tighten any loose connections and clean all contact surfaces.
Voltage drop is particularly common on longer trailers or when using undersized wiring. As electricity travels through wire, resistance causes some voltage loss. If your trailer uses thin wires or has lights positioned far from the plug connection, the voltage reaching those lights may be insufficient for proper brightness. This issue is compounded when you’re running multiple lights simultaneously. The solution is to upgrade to heavier gauge wiring that can carry the current with minimal voltage loss.
Flickering can also result from movement in the plug connection while towing. The constant vibration and jarring from road surfaces can cause intermittent contact if the plug isn’t secured properly or if the socket has worn loose. Some people find that wrapping electrical tape around the connection helps, but a better solution is to ensure you have a quality plug and socket combination that fits snugly together.
Important Maintenance Considerations
Regular Inspection and Cleaning
Prevention is always better than roadside repairs. Make it a habit to inspect your trailer lights before every significant journey, especially if the trailer has been sitting unused for a while. Auckland’s coastal environment is particularly harsh on electrical connections, with salt air accelerating corrosion. Even if you don’t use your trailer near the water, moisture from rain and humidity can cause problems over time.
Clean your plug and socket connections at least every few months, or more frequently if you’re a regular trailer user. Disconnect the plug and use contact cleaner or methylated spirits on a cloth to remove any grime or light corrosion. Once everything is clean and dry, apply a thin layer of dielectric grease or lanolin-based spray to protect against moisture. This simple maintenance step can prevent most connection-related problems.
Don’t forget to check the light lenses themselves. Cracked or broken lenses allow water to enter the light assembly, which quickly leads to bulb failure and corroded connections. Replace any damaged lenses promptly, and consider upgrading to sealed LED units if you’re experiencing ongoing problems with water ingress.
Understanding New Zealand’s Legal Requirements
Operating a trailer with faulty lights on Auckland roads is illegal and can result in fines and demerit points. Your trailer must have functioning brake lights, indicators, tail lights, and a number plate light. If your trailer is wider than your vehicle, you may also need side marker lights. Police and transport enforcement officers regularly check trailers, particularly during holiday periods when more recreational trailers are on the road.
Beyond the legal requirements, working trailer lights are essential for safety. Other drivers rely on your lights to know when you’re braking, turning, or simply present on the road ahead. This is especially important during Auckland’s unpredictable weather conditions, early morning commutes, or evening drives when visibility is reduced. Taking the time to maintain your trailer lighting isn’t just about avoiding fines, it’s about protecting yourself and everyone else sharing the road.
When to Upgrade Your Wiring System
If you find yourself constantly battling trailer light problems, it might be time to consider a complete wiring upgrade. Older trailers often have basic wiring that was never designed to last decades. Modern waterproof wiring looms with properly sealed connectors can eliminate most common issues. LED lights are also worth considering as they draw less current, last significantly longer than traditional bulbs, and are much more resistant to vibration and impact damage.
Some vehicles require a dedicated trailer wiring harness that integrates with the vehicle’s computer system rather than tapping directly into the existing light circuits. This is particularly common with newer European vehicles. These systems use a control module that prevents electrical issues from damaging your vehicle’s sensitive electronics while ensuring proper function of all trailer lights. While more expensive initially, they provide reliable operation and protect your vehicle’s warranty.
Need Help with Your Trailer Light Problems?
Troubleshooting trailer light issues requires patience and a systematic approach, but most problems can be resolved with basic tools and some electrical knowledge. Regular maintenance and prompt attention to problems will keep your trailer lights functioning reliably for years to come.
As auto electricians in Auckland, we can help you diagnose and repair any trailer lighting problems quickly and effectively. Whether you need a complete rewiring, proper installation of a tow bar lighting system, or just can’t figure out why your lights aren’t working, our team has the expertise to get you back on the road safely. Contact our team today by calling 09 218 7789.