2020 International LT Bulb Size Guide: Headlight, Tail, Fog & More

As an ASE-certified master technician who has worked extensively on heavy-duty commercial vehicles, I know how critical proper lighting is for your 2020 International LT. Whether you are managing a fleet or operating as an owner-operator, a burnt-out headlight or marker light isn't just a safety hazard—it’s an easy way to fail a DOT inspection and lose valuable time on the road.

The 2020 International LT series offers a mix of traditional halogen and modern factory LED lighting, depending on the trim and spec sheet ordered by the original buyer. Below is a comprehensive guide to the bulb sizes and types used on this truck to help you get back on the road quickly.

Quick Reference: 2020 International LT Bulb Sizes

Note: Many 2020 International LTs were spec'd with factory sealed LED assemblies for exterior lighting. If your truck has factory LEDs, the entire housing or module must be replaced rather than an individual bulb.

LED vs Halogen Upgrade Considerations

If your International LT came equipped with standard halogen headlights (H11 low beams and 9005 high beams), upgrading to aftermarket LED bulbs is a highly popular modification to improve nighttime visibility and reduce driver fatigue. However, commercial trucks have specific electrical systems that require careful attention:

• CANBUS Errors: The LT's multiplexed electrical system monitors bulb resistance to alert you of burnouts. Installing low-draw LED bulbs into a halogen circuit will frequently trigger dashboard warnings or cause the lights to flicker. You will likely need CANBUS adapters (load resistors or decoders) inline with your new LEDs to spoof the factory resistance.
• Clearance and Heat: High-output LED bulbs utilize cooling fans or large heat sinks. Ensure there is enough clearance behind the headlight housing to accommodate these bases and that the dust caps can still be securely sealed to prevent moisture intrusion.
• Vibration Resistance: Heavy-duty trucks experience severe vibrations. Always invest in premium LED kits with solid-state designs and secure locking collars. Cheap bulbs will rattle loose or fail prematurely on rough highways.

How to Replace Each Bulb

• Headlights (Low/High/Fog): The International LT features a relatively mechanic-friendly hood design. Once the hood is tilted open, you can access the rear of the headlight assemblies. Twist off the protective dust cover, unclip the wiring harness, and twist the bulb counterclockwise to remove it. When installing the new bulb, never touch the glass of a halogen bulb with your bare hands, as oil will cause it to shatter.
• Front Turn Signals / DRLs: Located within the main headlight assembly on halogen models. Access them from behind the housing. Twist the socket out, pull the old 3157/4157 bulb straight out, and push the new one in.
• Rear Lighting (Stop/Tail/Turn/Reverse): Most LT rear light bars utilize standard 4-inch round rubber grommet sealed LED lights. To replace these, simply unplug the 3-prong pigtail from the back and pry the light assembly out of the rubber grommet with a flathead screwdriver. If your setup uses standard boxes, remove the screws holding the red/clear lens to access the 3157/3156 bulbs.
• Side Markers / Cab Lights: Sun visor and fairing marker lights are usually sealed factory LED units secured by two Torx or Phillips screws. Unplug the pigtail and swap the whole unit.
• Interior Dome Lights: Use a plastic trim tool to gently pop off the overhead console lenses to access the festoon (211-2) or wedge (194) bulbs.

Common Lighting Issues for this Generation

The 2020 International LT multiplex electrical system (often governed by the body control module) is generally reliable, but wiring chafing is a known issue. The wiring harnesses near the front bumper and wheel wells can rub against the frame due to engine vibration, leading to shorts or intermittent headlight/fog light failures. Furthermore, the factory halogen headlight housings are susceptible to moisture buildup if the rear dust caps are not perfectly sealed during bulb replacements, leading to premature bulb burnouts and cloudy lenses.

Don't let a lighting issue keep your truck off the road or risk a DOT violation. Find a trusted shop on Repairius.