2019 Freightliner M2 106 Bulb Sizes (Headlight, Tail, Fog)

As an ASE-certified master technician, I’ve serviced countless commercial trucks, and the 2019 Freightliner M2 106 is one of the most common medium-duty platforms on the road today. Because these trucks are heavily customized by upfitters for everything from box trucks to tow rigs, lighting can vary—especially at the rear. However, the cab and chassis front-end lighting remains relatively standard.

Whether you're managing a fleet or operating as an owner-operator, keeping your M2 106’s lights fully operational is critical for DOT compliance and safety. Below is the comprehensive bulb size guide for the 2019 Freightliner M2 106.

Quick reference

Note: Rear lighting (tail, brake, turn, reverse) often depends on the custom upfitter body. The sizes below represent the most common chassis-cab standard setups.

LED vs halogen upgrade considerations

Upgrading a 2019 Freightliner M2 106 from factory halogen or incandescent bulbs to LEDs is highly recommended for commercial applications due to the extended lifespan and superior visibility. However, there are a few important considerations:

• CANBUS and Flasher Relays: If you upgrade your front or rear turn signals to LED, you may experience "hyper-flashing" because LEDs draw significantly less power than incandescents. You will likely need to install load resistors or upgrade the heavy-duty flasher relay under the dash to an LED-compatible unit.
• Sealed Beam vs. Composite Upgrades: If your M2 106 has the basic rectangular sealed beam headlights (H6054), the best upgrade is replacing the entire 200mm housing with a DOT-compliant sealed LED headlamp. If you have the aerodynamic composite housings, you can install H4 LED drop-in bulbs. Make sure the LED bulb has a slim heatsink, as space behind the composite housing can be somewhat restricted by chassis wiring.
• Upfitter Bodies: When upgrading rear lights on a box or flatbed, it is usually best to replace the entire 4-inch round or 6-inch oval grommet-mounted fixture with a sealed LED unit rather than replacing standard bulbs within an old, weather-beaten housing.

How to replace each bulb

Here are a few technician tips for replacing the most common bulbs on your Freightliner:

• Headlights (Composite): Tilt the hood forward. The back of the headlight housing is completely exposed and easily accessible. Unplug the H4 harness, pull off the rubber dust boot, unclip the metal retaining spring, and swap the bulb. Do not touch the new halogen glass with your bare fingers.
• Headlights (Sealed Beam): Remove the Torx or Phillips screws holding the metal bezel in place, then remove the retaining ring screws. Pull the entire glass housing forward and unplug the 3-prong connector.
• Front Turn Signals: Located in the lower bumper or the side of the headlight housing (depending on trim). You can reach behind the bumper or housing, twist the socket counterclockwise, and pull it out.
• Cab Marker Lights: These require getting up on the roof. Unscrew the two screws holding the amber lens. On newer models, these might be entirely sealed LED units that require replacing the whole fixture and splicing the two wires. If it's the older style, it just takes a simple 194 wedge bulb.
• Rear Lighting: For standard chassis tail lights, use a screwdriver to remove the lens cover to access the 3157 bulbs. If your truck has a commercial body with rubber-grommet lights, simply pry the light assembly out of the rubber grommet with a flathead screwdriver and unplug the 3-pin standard pigtail in the back.

Common lighting issues for this generation

• Corroded Grounds: Commercial trucks face harsh environments. If your turn signals are acting erratic or your headlights are dim, check the main ground points on the front chassis frame.
• Moisture in Composite Housings: The aerodynamic composite headlight housings on the M2 are known to develop micro-cracks or lose their seal over time, leading to condensation. If a new rubber dust boot doesn't fix it, the entire housing will need to be replaced to prevent bulb blowouts.
• Upfitter Wiring Chafing: Because the rear wiring is often routed by a third-party body builder, the harness running along the frame rails can rub against crossmembers. If you lose all rear tail lights, trace the harness from the rear axle forward, looking for chafed wires or blown inline fuses.

Keeping your Freightliner M2 106 properly lit is non-negotiable for commercial safety. If you are dealing with complex wiring gremlins or need a DOT inspection, don't leave it to chance. Find a trusted shop on Repairius.