MOT & Side-Marker Lights: The Full Guide

When it comes to the annual MOT test, vehicle lighting often causes a great deal of confusion for motorists across the UK. With so many different types of lights on modern vehicles, understanding which ones are inspected, and to what standard, can feel like navigating a dimly lit maze. One particular area of ambiguity frequently arises regarding side-marker lights. Are they part of the MOT test? And what happens if your vehicle's general 'side lights' fail to illuminate? This extensive guide aims to clarify these points, providing a detailed understanding of vehicle lighting requirements for the MOT and offering practical advice for common lighting issues.

Side-Marker Lights vs. Side Lights: Understanding the Distinction

Before diving into the specifics of the MOT, it's crucial to differentiate between 'side-marker lights' and what are commonly referred to as 'side lights' in the UK. The terminology can be a source of misunderstanding, leading to incorrect assumptions about vehicle compliance.

• Side-Marker Lights: These are amber lights typically found on the sides of longer vehicles, such as lorries, buses, and larger trailers. Their primary purpose is to indicate the overall length of the vehicle to other road users, particularly at night or in poor visibility. They become mandatory when a vehicle exceeds a certain length, as dictated by Construction and Use Regulations. For most standard passenger cars, side-marker lights are not fitted as standard and are not required.
• Side Lights (Position Lamps): Often called 'parking lights' or 'position lamps', these are the low-intensity lights at the front (white) and rear (red) of your vehicle that are designed to make the vehicle visible when parked or when driving in conditions that don't warrant full headlights, such as dusk or light rain. These are a fundamental safety feature for all vehicles and are distinct from side-marker lights.

Are Side-Marker Lights Part of the MOT Test?

This is a question that frequently surfaces, and the answer, for most everyday vehicles, might surprise you. According to the official MOT Inspection Manual, side-marker lights are generally not part of the standard MOT inspection for most passenger vehicles (Class 3, 4, 5, and 7). The manual primarily focuses on the inspection of front and rear position lamps, headlamps, stop lamps, indicators, and fog lights.

The manual states that front and rear position lamps are covered in Section 1.1, among other critical lighting components. While side-marker lights are indeed a legal requirement for certain vehicle types based on their length, their operation is not explicitly listed as an inspection item for the vast majority of vehicles undergoing an MOT. This means that if your standard car, which isn't required to have side-marker lights by law, happens to have them fitted (perhaps as an aftermarket addition or a feature on a very long model), their functionality might not be scrutinised during the MOT. However, it's always best practice for any fitted light to be operational. If a light is fitted and clearly broken or obscured, it could still be a reason for an advisory or even a failure under general condition rules, though this is less common for side-markers.

Why Side Lights (Position Lamps) Are Critical for MOT

While side-marker lights may not be a primary MOT concern for many, your vehicle's standard side lights (position lamps) are absolutely crucial. They are fundamental to your vehicle's visibility and safety. A failure of any position lamp is a definite MOT fail. The MOT tester will check:

• Presence and Position: Are they fitted correctly and in the right place?
• Condition: Are they free from damage, cracks, or discolouration that would impair their function?
• Operation: Do they illuminate correctly and consistently?
• Colour: Are the front lamps white and the rear lamps red?
• Pairing: Are both lamps on each side working (e.g., both front side lights, both rear side lights)?

If either of your front or rear side lights is not working, your vehicle will fail its MOT. This highlights the importance of regular checks of all essential lighting components.

Troubleshooting Common Side Light Failures

It's incredibly frustrating when your side lights stop working, especially if both go out simultaneously. This often indicates a common fault rather than an isolated bulb issue. Here's a systematic approach to troubleshooting:

1. Check the Bulbs

While it's less likely for both bulbs to fail at precisely the same time, it's not impossible. A simple visual inspection can confirm if the filament is broken. If one side light works and the other doesn't, a blown bulb is the most probable cause. If neither is working, proceed to the next steps.

2. Inspect the Fuses

This is often the culprit when multiple lights or an entire circuit stops working. Vehicle lighting circuits are protected by fuses to prevent damage from electrical overloads. Your vehicle's owner's manual will have a diagram showing the location of the fuse box (often under the bonnet or in the passenger footwell) and which fuse corresponds to your side lights. Look for a blown fuse – the small wire inside will be broken. Replace it with a fuse of the correct amperage. Never use a higher amperage fuse, as this can cause serious electrical damage or even a fire.

Common Fuse Box Locations:

• Under the bonnet (engine compartment)
• Inside the cabin (e.g., behind a panel in the dashboard, glove box, or footwell)
• In the boot (on some vehicles)

3. Examine the Wiring

Damaged or corroded wiring can interrupt the electrical flow to your lights. Look for any visible signs of fraying, cuts, or corrosion on the wires leading to the side light bulb holders. This can be more challenging to diagnose without specific tools like a multimeter, but a visual check is always a good starting point. Check for loose connections at the bulb holder itself.

4. Test the Bulb Holders

Sometimes, the issue isn't the bulb or the fuse, but the bulb holder itself. Corrosion on the contacts within the holder can prevent a good electrical connection. Gently clean the contacts if you see any signs of rust or dirt. You can also use a multimeter to check for voltage at the bulb holder when the side lights are switched on.

5. Check the Light Switch

While less common, a faulty light switch on your dashboard or steering column can prevent the side lights from activating. If other lights controlled by the same switch (like headlights) are working, it might indicate a specific fault within the side light circuit of the switch. This usually requires professional diagnosis.

6. Earth Faults

A poor earth connection can also lead to lights not working or working intermittently. All electrical components need a good earth return path to function. If the earth wire for the side light circuit becomes loose or corroded, the lights won't work. Tracing earth points can be tricky and may require professional assistance.

Table: Vehicle Lights and MOT Relevance

To help clarify the importance of various lighting components for your MOT, here's a comparative table:

Performing Your Own Pre-MOT Lighting Checks

To avoid the disappointment and cost of an MOT retest, a thorough pre-MOT lighting check is one of the easiest and most effective things you can do. It takes mere minutes and can save you a lot of hassle.

1. All External Lights: Turn on your side lights, then dipped beam, then main beam. Walk around the vehicle and check every single bulb is working: front side lights, headlights (both dipped and main), indicators (front, side repeaters, rear), rear side lights, brake lights (get someone to press the pedal for you), reverse light(s), rear fog light(s), and number plate lights.
2. Indicator Flash Rate: Ensure your indicators flash at a consistent and normal rate. If they flash rapidly, it usually indicates a blown bulb on that side.
3. Headlight Aim: While difficult to perfectly check without specialist equipment, you can do a rough check against a wall in the dark. The beams should be level and not pointing excessively up or down, or wildly to one side.
4. Clean Lenses: Ensure all light lenses are clean and free from dirt, cracks, or condensation that could obscure the light output.
5. Dashboard Warning Lights: Check for any bulb failure warning lights on your dashboard.

Frequently Asked Questions About Vehicle Lighting and MOT

Q: Can a single blown bulb cause an MOT failure?

A: Yes, absolutely. For any mandatory light (such as side lights, headlights, brake lights, indicators, fog lights, or number plate lights), a single non-working bulb will result in an MOT failure. Even if the other bulb in a pair is working, the failure of one is enough.

Q: My side light fuse keeps blowing. What could be wrong?

A: A fuse that repeatedly blows indicates an underlying electrical fault, most commonly a short circuit somewhere in the wiring. This means the live wire is coming into contact with an earth point or another wire it shouldn't, causing an excessive current draw that blows the fuse. This requires professional diagnosis to trace and repair the short, as it can be difficult to locate.

Q: Is it okay if my side lights are a different colour?

A: No. Front position lamps must emit white light, and rear position lamps must emit red light. Any deviation from these colours (e.g., blue, green, or even amber for position lamps) will result in an MOT failure, as it is illegal and confusing to other road users.

Q: What's the difference between side lights and daytime running lights (DRLs)?

A: Side lights (position lamps) are low-intensity lights intended for use in low light conditions or when parked. DRLs are brighter lights designed to make your vehicle more visible during daylight hours. While DRLs are often on automatically, they are not an MOT testable item, whereas side lights are.

Q: How often should I check my vehicle's lights?

A: It's highly recommended to check all your vehicle's external lights at least once a week, or certainly before any long journey. Bulbs can fail at any time, and regular checks ensure you remain safe and compliant on the road.

Conclusion

While the specific role of side-marker lights in an MOT test might be minimal for most passenger vehicles, the broader category of vehicle lighting is paramount. Your side lights (position lamps), along with headlights, brake lights, and indicators, are fundamental safety features that are rigorously checked during the MOT. Understanding the distinction between different light types and knowing how to perform basic troubleshooting and pre-MOT checks can save you time, money, and hassle. Regular maintenance and prompt attention to any lighting issues will not only help your vehicle pass its MOT but, more importantly, ensure your safety and the safety of others on the road.

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