Do side markers have to light up?
Yes, in most cases side marker lamps are required to illuminate when the vehicle’s exterior lights are on. The exact rules depend on vehicle type, width, and jurisdiction.
Legal baseline: when side markers are required
In the United States, federal safety standards under FMVSS 108 govern side marker lamps. Broadly, vehicles that are 80 inches wide or more and manufactured after September 1, 1968 must include side marker lamps and reflectors on both sides. Colors and placement are standardized: amber for the front side markers and red for the rear side markers. In operation, the markers are designed to illuminate along with the vehicle’s exterior lighting rather than remain lit on their own.
Key points and definitions
Before outlining the core requirements, here is a concise overview of how the rules typically apply. The following items summarize the most common scenarios regulators reference.
- Scope and applicability: Side marker lamps are generally required on motor vehicles over 80 inches wide and on trailers and commercial vehicles that meet width or GVWR criteria. Some narrow or older vehicles may be exempt or use integrated lighting.
- Color and placement: Front side markers typically use amber lenses; rear side markers use red lenses. Lamps are placed on the sides to improve horizontal visibility; reflectors may accompany the lamps where required.
- Activation: Side markers must illuminate when the vehicle’s exterior lighting is on (headlights or parking lights). Some systems may also support daytime lighting if the vehicle is equipped and compliant.
- Trailers and towables: Most trailers and semi-trailers meeting the width or GVWR thresholds must include side marker lamps and reflectors, wired to the towing vehicle’s electrical system.
- Enforcement and compliance: Vehicle inspections and road use enforcement check that side markers function properly; noncompliance can lead to fines, failed inspections, or recalls in some cases.
In practice, most modern vehicles sold in the United States and Canada follow these standards, but there are exceptions and regional rules that can affect individual models.
Regional variations and exceptions
Beyond the U.S. baseline, rules differ by region, vehicle class, and use case. The following outlines how some areas approach side marker lighting.
Regional scope
- Canada: The CMVSS 108 standard mirrors the general approach of FMVSS 108, with similar requirements for side marker lamps on applicable vehicles and trailers, including color and activation rules.
- European Union and United Kingdom: Many passenger cars do not rely on separate side marker lamps; side signaling is typically handled by integrated front/rear lighting and turn indicators. Some commercial vehicles and caravans/trailers still require side marker lighting in certain jurisdictions.
- Other regions: Some countries require side markers or side reflectors on trailers, caravans, or heavy vehicles, while others have different conventions for lighting color and activation. Always check local regulations when importing or modifying a vehicle.
Regional rules vary widely, so it’s important to verify requirements with local motor-vehicle authorities or a qualified installer, especially if you operate across borders or use specialized equipment.
What to do if your side markers don’t light
If a side marker fails to illuminate, it can affect visibility and regulatory compliance. Here are steps to diagnose and fix common problems.
Troubleshooting steps
- Inspect the bulb or LED module for burnout or failure; replace with the correct type (amber front, red rear) as specified for the marker.
- Check fuses and relays in the vehicle’s fuse box; replace any blown fuses and test the circuit.
- Inspect wiring and connectors for damage, corrosion, or loose connections; repair or replace as needed.
- Test for power at the marker with a test light or multimeter; verify the ground is solid and there is a return path.
- For trailers, verify the tow vehicle’s wiring harness and the trailer connector are correctly wired and grounded; test the circuit with the trailer connected.
- If the problem persists, consult a qualified automotive technician or dealership; driving with faulty side markers can be unsafe and may fail inspections.
Regular maintenance and timely replacements help keep markers compliant and reliable on the road.
Practical tips for installation and maintenance
Owners and installers can reduce failure risk by following best practices for installation, brightness, and durability.
Best practices
- Use DOT-approved lighting modules that meet FMVSS 108 standards to ensure compliance and consistent brightness.
- Ensure correct color and placement: amber front side markers and red rear side markers; keep lenses clean and free of cracks.
- Seal and protect connectors to prevent moisture ingress; check for corrosion during routine maintenance.
- For trailers, confirm proper grounding and a reliable power connection to the tow vehicle’s lighting circuit.
Quality installation and periodic checks reduce the likelihood of failures and help ensure ongoing compliance during inspections.
Summary
Side markers are a functional safety feature that, in many places, are legally required to light up when exterior lights are on. In the United States, FMVSS 108 sets out width-based applicability, color conventions, and activation rules that apply to most vehicles 80 inches wide or more and to many trailers. Regional variations exist, with Canada generally aligned with the U.S. standard and Europe often treating side markers differently, particularly for passenger cars. If a side marker isn’t lighting, check the bulb/LED, fuses, wiring, ground, and trailer connections, and seek professional help if needed. Regular maintenance helps vehicles stay visible, compliant, and roadworthy.
