2018 International LT — Bulb Sizes (Headlight, Tail, Fog)

As an ASE-certified master technician, I know that keeping the lights functioning correctly on a Class 8 heavy-duty truck like the 2018 International LT is critical for safety and DOT compliance. Fleet managers and owner-operators alike need quick, accurate information when a light goes out on the road. The 2018 International LT comes with either standard halogen headlight assemblies or premium full-LED assemblies depending on how the truck was spec'd from the factory.

Below is the comprehensive guide to replacing the bulbs on your 2018 International LT, including upgrade tips and common issues.

Quick reference: 2018 International LT Bulb Sizes

Note: Many 2018 International LTs feature completely sealed LED assemblies for the headlights and tail lights. If your truck is equipped with OEM LEDs, individual bulbs cannot be replaced; the entire housing must be swapped.

LED vs halogen upgrade considerations

Upgrading from standard halogens to LEDs is incredibly popular for over-the-road trucks due to the increased visibility and reduced strain on the electrical system. However, there are a few things to keep in mind:

• CANBUS Errors & Flickering: The International LT's Body Control Module (BCM) monitors electrical draw to alert you to burnt-out bulbs. Because LEDs draw significantly less power than halogens, the BCM might trigger a "bulb out" warning on the dash or cause the lights to flicker. You will likely need LED bulbs with built-in CANBUS decoders or inline load resistors to trick the system.
• Housing Clearance: The headlight housings on the LT are relatively tight. When buying LED replacement bulbs for H11 or 9005 slots, ensure the heat sink or cooling fan on the back of the LED bulb is compact enough to allow the dust cover to close completely. Moisture intrusion is a death sentence for electrical connections.
• Beam Pattern: Always ensure your LED bulbs are clockable (adjustable). The diodes should face exactly 3 o'clock and 9 o'clock in the housing to mimic the halogen filament and prevent blinding oncoming traffic.

How to replace each bulb

• Headlights (Low/High Beam): Access the back of the headlight assembly by tilting the hood forward. Twist the circular dust cover counterclockwise to remove it. Twist the H11 or 9005 bulb counterclockwise, unplug the harness, and swap the bulb. Be sure not to touch the new halogen glass with your bare hands.
• Front Turn Signal / DRL: Accessible from behind the headlight housing while the hood is open. Twist the bulb socket out and pull the wedge bulb straight out.
• Fog Lights: These are located in the lower bumper. You can usually reach behind the bumper to twist the H8 bulb out. If equipped with sealed LEDs, two retaining bolts hold the housing in place.
• Rear Tail / Brake / Turn / Reverse: Heavy trucks typically use standard 4-inch round rubber grommet mounts for the rear lights. If it's a sealed LED (most common), simply pry the light assembly out of the rubber grommet with a flathead screwdriver, unplug the 3-prong pigtail, and push the new unit in.
• Cab Clearance / Marker Lights: These usually require a Phillips screwdriver to remove the small lens on the top of the cab or the side fairings. Pull the 194 wedge bulb straight out.
• Interior Dome/Map: Use a plastic trim tool to gently pop off the clear plastic covers on the overhead console. The festoon-style (578) or wedge bulbs pull right out.

Common lighting issues for this generation

The 2018 International LT is a workhorse, but it has a few known electrical quirks when it comes to lighting. Wiring harnesses near the front bumper (particularly for fog lights and lower marker lights) are exposed to road salt and debris, leading to corrosion at the connectors. If a new bulb doesn't fix your outage, check the pigtail for green corrosion or broken ground wires.

Additionally, OEM LED headlight assemblies are known to occasionally suffer from moisture buildup if the rear seals are compromised, which can short out the internal boards. Since these units are sealed, a replacement of the entire expensive assembly is required if this happens.

If you are dealing with persistent electrical issues, BCM faults, or wiring harness damage that goes beyond a simple bulb swap, don't leave it to chance. Find a trusted shop on Repairius.