Light Checks

headlights on

One of the most common DOT violations are lighting defects or faults. While the technology has improved, the problem hasn’t gone away. A bad turn signal is an automatic Out-Of-Service (OOS) violation.

In addition to having a turn signal out on either side, other DOT OOS violations for lighting occur when:

  • Both headlamps are inoperative
  • Both tail lamps are inoperative, or
  • Both stop lamps are inoperative

What to do to avoid lighting problems?

The electrical system, like any other system, needs proper care and maintenance. This means having a preventative maintenance system in place, properly documenting inspections and maintenance, and focusing on proactive, not reactive, measures, as in replacing lamps or bulbs at the first signs of corrosion, not when they already don’t work anymore.

Tip 1. Don’t start the engine with the lights on.

Starting the engine with the lights on creates a draw on the electrical system that can burn out bulbs or cut bulb-life in half. Shut your lights off before engaging the starter or jump-starting the vehicle.

Tip 2. Spec replacement lamps properly.

A bulb or lamp is a bulb or lamp . . . right?  Not every time. Be extra careful here.

Make sure the correct lamp or bulb is going into the correct socket. Do not attempt to “upgrade” the lighting system by replacing, for example, a Halogen bulb with a high intensity discharge (HID) bulb. Even if the bulbs look alike, fit in the same headlamp, have the same wattage rating and seem to be completely interchangeable, switching the bulbs could result in an “optical mismatch,” bad lighting results, and may even be illegal.

The beam aim and pattern should not change when a bulb is replaced. This can happen if an improper bulb or a low quality replacement bulb is installed. A cheap or improper bulb could result in glare for opposing drivers and/or be illegal.

Ensure the bulbs or lenses are marked “DOT,” if *required. Headlamp bulbs are sometimes checked for the required “DOT” markings as part of a DOT vehicle inspection program.

*No marking is required by NHTSA (108) except for headlights and conspicuity tape

Tip 3. Don’t directly touch the bulbs/lamps during installation.

Fingertips contain oils which can burn onto the bulb. Protect the lamps/bulbs from contamination during installation. This will help extend the bulb’s service life.

Tip 4. Upgrade to LED stop, turn and tail lights.

LED lights have a longer life than filament bulbs and, because there is no filament, light up quicker. Use of LEDs could result in a higher level of safety performance and much longer service life cycles.

Tip 5. Use dielectric grease on the pigtail and/or other connections.

Dielectric grease helps to keep moisture, road chemicals, and resulting corrosion out of the electrical connections, ECM connectors, or connections. Corrosion is one of the major causes of truck light or electrical failures.


Lighting is one of the top areas of vehicle inspection violations. But you can proactively keep your lighting system in good working order with a preventative maintenance program, proper spec’ing of replacement parts, and following some of the above installation tips. This will result in fewer roadside inspections, less downtime, and best of all, a higher level of safety performance.

To learn more, see CMV Safety Inspection and Load Securement.

Thank you for reading this.