05/09/2007
Whilst often overlooked, the humble number plate bulb plays a crucial role in ensuring your vehicle remains road-legal here in the UK. Though it won't impact your car's performance or handling, a malfunctioning bulb can lead to frustrating dashboard error messages and, more significantly, an MOT failure. The good news? Replacing them is a remarkably straightforward task that most car owners can tackle with minimal fuss. Whether you're aiming to upgrade to a brighter, more efficient LED bulb or simply need an OEM replacement, this guide will walk you through everything you need to know, from understanding their importance to a step-by-step replacement process.
The Critical Role of Number Plate Bulbs
It might seem like a minor detail, but illuminated number plates are a legal requirement for all vehicles on UK roads. This isn't just a bureaucratic formality; it's a matter of public safety and law enforcement. Police officers and ANPR (Automatic Number Plate Recognition) cameras rely on clearly visible registration plates to identify vehicles, especially in low-light conditions. Without functioning number plate lights, your vehicle becomes harder to identify, which can have implications for everything from traffic enforcement to accident investigation.
MOT Implications: Don't Get Caught Out!
The importance of these bulbs is underscored by their inclusion in the annual MOT (Ministry of Transport) test. If one or more of your number plate bulbs are not working, your vehicle will automatically fail its MOT. Specifically, section 4.7.1 of the MOT manual dictates that all rear registration plate lamps must be present, working, and emit a white light. This immediate failure can lead to inconvenience, retest fees, and potentially a delay in getting your vehicle back on the road. Regularly checking these bulbs, particularly before your MOT is due, can save you a significant amount of hassle and expense.
Choosing the Right Number Plate Bulb
When it comes to selecting a replacement bulb, you'll find a variety of options available. The majority of number plate bulbs are what are known as "Festoon" bulbs. These are cylindrical bulbs with a contact point at each end, designed to slot into a spring-loaded holder. However, the term "Festoon" covers a range of sizes and technologies.
Types of Number Plate Bulbs: Halogen vs. LED
Historically, most vehicles came equipped with standard halogen festoon bulbs. These are incandescent bulbs that produce a warm, yellowish light. They are generally inexpensive and widely available, serving as a reliable OEM replacement. However, in recent years, LED (Light Emitting Diode) bulbs have become increasingly popular for number plate illumination. LEDs offer several advantages:
- Brighter Output: They typically emit a much brighter, whiter light, enhancing visibility.
- Energy Efficiency: LEDs consume significantly less power than halogen bulbs, reducing the load on your vehicle's electrical system.
- Longevity: They boast a much longer lifespan, often lasting many years, which means fewer replacements.
- Modern Aesthetic: Their crisp, white light often matches modern headlight designs, providing a more consistent look.
When upgrading to LEDs, it's crucial to consider CANBUS compatible bulbs. Many modern cars feature a CANBUS (Controller Area Network Bus) system that monitors the electrical current flowing through various circuits, including light bulbs. If you install a standard LED bulb (which draws much less power than a halogen), the CANBUS system might interpret this reduced current as a faulty bulb, triggering an error message on your dashboard. CANBUS-compatible LEDs have built-in resistors to mimic the electrical load of a halogen bulb, preventing these error messages.
Getting the Size Right: Millimetres Matter!
While most festoon bulbs look similar, they come in a variety of lengths. Even a minimal difference of a few millimetres can mean the bulb won't fit or won't make proper contact. Common sizes range from 31mm to 38mm, but other lengths exist. To ensure you purchase the correct size, consult one of the following resources:
- Your Car's Handbook: The most reliable source, your owner's manual will often list the specific bulb types and sizes for all exterior lights.
- Online Car Checker Tools: Many automotive parts retailers offer online tools where you input your vehicle registration number, and it provides a list of compatible parts.
- Enthusiast Forums: Vehicle-specific online forums are a treasure trove of information, often with members who have already performed these upgrades or replacements and can offer precise details.
- Measure the Old Bulb: Once you've removed the old bulb, you can carefully measure its length with a ruler.
Comparative Table: Halogen vs. LED Number Plate Bulbs
To help you decide, here's a quick comparison:
| Feature | Standard Halogen Festoon | LED Festoon (CANBUS Compatible) |
|---|---|---|
| Light Output | Warm, yellowish, moderate brightness | Bright, crisp white light |
| Energy Consumption | Higher | Significantly lower |
| Lifespan | Shorter (approx. 500-2,000 hours) | Much longer (approx. 20,000-50,000 hours) |
| Cost | Lower upfront cost | Higher upfront cost |
| Dashboard Errors | Rarely causes errors | Potential for errors if not CANBUS compatible |
| Durability | Filament susceptible to vibration | More resistant to shock and vibration |
What You Will Need for the Replacement
Gathering your tools beforehand will make the replacement process much smoother. You'll likely need very few items:
- Screwdriver or Drill: Depending on the type of screws holding your number plate light holders in place, you'll need a suitable Phillips, flathead, or Torx screwdriver. A low-speed drill with the correct bit can speed things up, but be gentle!
- Your Bulb of Choice: The new replacement bulb(s) you've carefully selected.
- Clean Cloth or Wipe: Useful for cleaning the bulb housing and avoiding transferring dirt or oils to the new bulb.
- Plastic Trim Removal Tool (Optional): In some vehicles, the light housing might be clipped in rather than screwed, or recessed in a way that benefits from a non-marring pry tool.
Step-by-Step Guide: How to Change Your Number Plate Bulb
The process is generally straightforward, but always proceed with care to avoid damaging delicate plastic parts or the electrical connections.
- Locate the Holders: Your number plate bulbs are typically housed in small plastic units, usually above or integrated into the rear number plate surround. There are often two separate units, one for each side of the plate.
- Unscrew the Holders: Using your screwdriver or drill, carefully remove the screws holding the light units in place. Be mindful not to overtighten them when putting them back, as this can strip the plastic. If there are no visible screws, the unit might be clipped in. In this case, gently pry around the edges with a plastic trim tool until it unclips.
- Access the Bulb: Once the holder is loose, it might either pull straight out, or you may need to twist it slightly to release it from its wiring harness. The bulb itself will be visible within the holder.
- Remove the Old Bulb: For festoon bulbs, simply pull the old bulb straight out of its spring-loaded clips. It might be a little stiff, but a gentle pull should suffice.
- Clean the Housing (Optional but Recommended): This is an excellent opportunity to clean out any dirt, moisture, or corrosion that may have accumulated inside the bulb holder. A clean cloth or cotton swab can be effective. This can help improve light output and ensure a good electrical connection for the new bulb.
- Insert the New Bulb: Carefully push the new bulb into the holder. Ensure it's seated firmly and correctly within the spring clips. Avoid touching the glass of a halogen bulb with bare hands, as oils can create hot spots and reduce its lifespan. LEDs are less sensitive to this.
- Test the Bulbs: Before fully reassembling, it's crucial to test your new bulbs. Turn on your vehicle's lights (usually the side lights or headlights) to confirm they illuminate correctly. If they don't, try flipping the LED bulb 180 degrees, as some LEDs are polarity sensitive. If it's still not working, double-check the connection and ensure the bulb isn't faulty.
- Screw the Holders Back In Place: Once you've confirmed both bulbs are working, carefully reattach the light units. Screw them back in gently, ensuring a snug fit without overtightening. If clipped in, push firmly until you hear a click.
Troubleshooting Common Problems
While changing number plate bulbs is usually a breeze, a few issues can arise. Knowing how to address them can save you further frustration.
Access Difficulties
Some car manufacturers seem to delight in making simple tasks unexpectedly challenging. You might find the screws are in an awkward position, or the entire light unit is deeply recessed. If you encounter significant difficulty accessing the holders, it's always best to consult your car's owner's manual. Failing that, searching online enthusiast forums for your specific make and model can often provide invaluable tips, diagrams, or even video guides from other owners who've faced the same challenge.
Incompatible Bulbs and Dashboard Errors
This is most common when upgrading to LED bulbs. As mentioned, if you install non-CANBUS compatible LEDs in a car with a CANBUS system, the car's computer may detect the lower power draw as a faulty bulb, triggering a "bulb out" warning on your dashboard. These warnings can be quite persistent and annoying.
- Flickering or Malfunctioning LEDs: Even if they light up, non-CANBUS LEDs might flicker, dim, or only work intermittently due to the car's electrical system not providing a stable current.
- Persistent Error Message: If you've replaced a faulty bulb and the error message remains, and you're certain the new bulb is working, there might be a deeper electrical issue.
- Using an OBD2 Scanner: In cases where the error persists despite new, working, and (if applicable) CANBUS-compatible bulbs, you may need to use an OBD2 scanner. This tool plugs into your car's diagnostic port (usually under the dashboard) and can read specific fault codes. These codes can pinpoint the exact nature of the electrical issue, which might range from a corroded wire to a problem with the car's Body Control Module (BCM). While the scanner itself won't fix the problem, it provides the diagnostic information needed for a more targeted repair.
Frequently Asked Questions About Number Plate Bulbs
Here are answers to some common queries regarding these small but important lights:
Q: How often should I check my number plate bulbs?
A: It's good practice to check all your exterior lights, including number plate bulbs, at least once a month. A quick walk-around your car with the lights on (and someone to help check the rear) can prevent unexpected MOT failures or fines.
Q: Can I use coloured number plate bulbs?
A: No. In the UK, number plate lights must emit a white light only. Using any other colour (e.g., blue, red) is illegal and will result in an MOT failure and potentially a fine.
Q: My number plate light is dim, but not out. What could be the cause?
A: A dim bulb can be a sign that it's nearing the end of its life, or it could indicate a poor electrical connection due to corrosion or dirt in the housing. Cleaning the contacts and replacing the bulb usually resolves this.
Q: Do I need to disconnect my car's battery before changing the bulbs?
A: While not strictly necessary for number plate bulbs, it's always a good safety practice when working with any electrical components on your car. If you're uncomfortable, or if the light unit is difficult to access, disconnecting the negative terminal of your battery can eliminate any risk of short circuits.
Q: I've replaced the bulb, but the error message is still there. What next?
A: First, ensure the new bulb is definitely working and, if upgrading to LED, that it's CANBUS compatible. If the error persists, it's advisable to use an OBD2 scanner to read the specific fault code. This will help diagnose whether the issue is indeed a bulb, wiring, or a deeper electrical fault that might require professional attention.
Conclusion
Replacing your number plate bulbs truly is one of the most straightforward car maintenance tasks you can undertake. It's a quick, inexpensive fix that not only keeps your vehicle road-legal but also prevents those annoying dashboard warnings and the potential for a costly MOT retest. Whether you opt for a basic, reliable OEM replacement or decide to upgrade to the brighter, longer-lasting efficiency of LED technology, you now have all the knowledge and steps required to complete the job with confidence. Remember, for the best and most reliable light output, always take the opportunity to give the bulb holders a good clean whilst they're accessible. A little bit of care goes a long way in ensuring your number plate remains clearly visible, day and night.
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