What Are Side Marker Lights?

by Chris Stevenson
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Side marker lights are illumination devices attached to the front and rear sides of motorized vehicles and trailers. They function as auxiliary safety lights that can be seen by other drivers when the vehicle operator turns on the headlights. They are standard equipment on most vehicles and can also be purchased and installed as aftermarket options.

Side Marker Function

Side marker lights provide extra illumination at night and during times of poor visibility to help other drivers and pedestrians see the vehicle. Side marker lights are standard equipment on buses, trailers, cars, trucks and some work and utility vehicles.


In the United States, side marker lights became a requirement on January 1, 1968, for vehicles that exceed 80 inches in length, including large buses and trucks. This requirement was extended on January 1,1969, for all other vehicles, including trailers, multi-purpose vehicles, motorcycles, cars and small trucks.

Side Marker Construction

Side markers usually consist of one, single-element bulb, either a carbon filament (hot) bulb or LED (light emitting diode), which is encased in a socket and small frame. The frame attaches directly to the vehicle's front fender and rear quarter panel with screws or snap retainers. In the United States, the lens of a side marker, made of high impact, translucent plastic, is amber-colored for the front of the vehicle and red for the rear.

Power Source

Side marker lights have single wires, usually of 16-gauge thickness, which lead from the bulb socket to the parking light wire, taillight or main headlight wire loom. They use the standard automotive 12 volts for operation and activate when the headlights are turned on.

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