Safety First: How Marker Lights Protect Your Fleet
It’s easy to overlook trailer marker lights — until one goes dark and risk lights up. These small but critical components aren’t just a DOT requirement — they’re your first defense against low-visibility collisions, roadside violations, and unnecessary downtime.
Trailer marker light safety starts with understanding their role, their inspection requirements, and the right tools to test them quickly and accurately. Fleets that treat marker lights like mission-critical safety features — because they are — reduce accident risk and keep equipment moving.
What Do Marker Lights Actually Do?
Marker lights are positioned around the edges of a trailer to signal its length, width, and height — especially in poor visibility conditions like fog, rain, darkness, or early dawn. They’re essential to:
Preventing collisions from passing vehicles
Signaling the trailer’s full dimensions at night
Meeting federal lighting requirements under FMVSS 108
Ensuring roadside inspectors see a properly lit trailer
Enhancing the driver’s visibility awareness in their mirrors
They’re small. But their failure creates a big safety gap — one that can expose your fleet to liability and your drivers to risk.
Common Causes of Marker Light Failure
Marker lights may fail for reasons that seem minor at first but build up over time:
Corroded connections or ground issues
Broken wires or harness damage
Moisture intrusion into light housings
Poor electrical continuity from the tractor
Vibration-related fatigue at connectors
And the worst part? You may not catch these failures during a walk-around or basic visual check — especially when dealing with intermittent issues.
Accurate Testing = Safer Trailers
To inspect marker lights effectively, fleets need more than just a flashlight and a mirror. Proper trailer marker light safety testing involves confirming:
Each light receives the correct voltage
Wiring continuity is intact
No shorts, opens, or feedback conditions exist
All required circuits function together under load
The Inspector 930 delivers all of this — with fast, one-person operation, pass/fail indicators, and full trailer circuit diagnostics. It eliminates guesswork and confirms every light is operational and properly powered.
DOT Compliance Starts Here
Improper or inoperative marker lights are a red flag during roadside inspections. They’re among the most common causes of lighting-related citations. Keeping them functional protects your CSA score, your equipment, and your bottom line.
By testing regularly and logging results, fleets can prove maintenance due diligence — and avoid costly surprises when pulled over or during internal audits.
One Tool to Keep Your Trailer Lit
The Inspector 930 was built to make trailer inspections fast, accurate, and consistent. With it, techs can identify faulty lights, trace wiring issues, and confirm full lighting system functionality — all without a tractor.
For a complete overview of how the Inspector 930 supports trailer marker light safety, visit lite-check.com/shop/inspector-930 or call 509-535-7512.