2018 Ford F-350 Super Duty Bulb Sizes

Quick Reference

The 2018 Ford F-350 Super Duty, a workhorse of a truck, came with a variety of lighting configurations depending on the trim level. While many F-350s rolled off the assembly line with traditional halogen lighting, higher trims such as the Lariat, King Ranch, and Platinum often featured more advanced LED or even HID (High-Intensity Discharge) systems for the headlights and fog lights. It's crucial to verify your specific truck's configuration before purchasing replacement bulbs.

For example, while the H11 and 9005 are common halogen sizes for low and high beams respectively, certain premium models were equipped with full LED headlight assemblies that do not have replaceable bulbs in the traditional sense, or HID projector headlights which use D3S bulbs for low beam and a separate halogen 9005 for high beam, or even full LED high beam. Similarly, fog lights could be H10 (also known as 9145) or H11 halogens, or integrated LED units. Daytime Running Lights (DRLs) were typically incandescent (4257NAK) in halogen-equipped trucks, but were integrated into the main LED headlight assembly on trucks with that option.

All external turn signals (front and rear), brake lights, and standard tail lights are typically incandescent bulbs (3457NAK for front turn, and 3157 for rear turn, brake, and tail). Reverse lights are commonly 921 bulbs. Interior lighting, including dome and map lights, typically uses incandescent bulbs like the 578 festoon bulb for the dome and 194 wedge bulbs for map lights and other smaller interior lights. License plate lights and side markers also commonly utilize 168 or 194 wedge bulbs.

LED vs Halogen Upgrade Considerations

Upgrading from halogen to LED bulbs in your 2018 F-350 Super Duty can significantly improve light output, modernize the look, and offer a longer lifespan. However, there are several important factors to consider:

• CANBUS Errors: Modern vehicles like the 2018 F-350 use a CANBUS (Controller Area Network Bus) system to monitor electrical components. LED bulbs draw significantly less power than halogens, which can trick the CANBUS system into thinking a bulb is out. This can cause "bulb-out" warning messages on your dashboard, hyper-flashing turn signals, or even prevent the lights from working correctly. To circumvent this, you'll often need CANBUS-compatible LED bulbs or separate load resistors (decoders) wired into the circuit. Ensure any aftermarket LEDs you purchase explicitly state they are CANBUS-ready for Ford Super Duty vehicles.

• Adapters and Fitment: While many aftermarket LED bulbs are designed to be "plug-and-play," some may require specific adapters or slight modifications for proper fitment within the headlight or taillight housing. Issues can arise with the depth of the LED bulb and its cooling fan interfering with the dust cap, or the bulb's base not seating correctly in the socket. Measure your available space and check product dimensions carefully.

• Beam Pattern: Not all LED replacement bulbs are created equal. Converting a halogen reflector housing to LED can sometimes result in a scattered or improper beam pattern, reducing effectiveness and potentially blinding oncoming drivers. Look for LED bulbs designed with optical properties that mimic the filament location of the original halogen to ensure a proper beam pattern.

• Flickering: In some cases, aftermarket LEDs can flicker due to voltage fluctuations or incompatibility with the vehicle's pulse width modulation (PWM) system. This is another area where CANBUS decoders or specific LED drivers can help.

How to Replace Each Bulb (Short Tips)

• Headlights (Low/High Beam): Access is typically from behind the headlight assembly. You may need to remove a plastic splash shield or move the battery/airbox for better access. Twist to unlock the bulb, unplug the connector, and reverse for installation. HID bulbs (if applicable) require extreme caution due to high voltage.

• Fog Lights: Most fog lights can be accessed from underneath the front bumper, often by reaching behind the bumper or removing a small access panel in the wheel well. Twist and pull to remove.

• DRL / Front Turn Signal: These are usually combined in one assembly and accessed from behind the headlight unit. Twist the socket to remove the bulb.

• Rear Turn Signal / Brake Light / Tail Light: Access is generally from inside the tailgate or through the side of the truck bed by removing the taillight assembly (typically two bolts on the inside edge). Once the assembly is out, twist the sockets to remove the bulbs.

• Reverse Lights: Also accessed by removing the taillight assembly and twisting the socket.

• License Plate Lights: Usually involves removing a couple of small screws from the clear lens cover above the license plate. Once the lens is off, twist the socket to access the bulb.

• Side Markers: Often simply pop out with a trim tool or require removal of a couple of small screws.

• Dome/Map Lights: Carefully pry open the clear lens cover using a plastic trim tool to avoid damaging the headliner or plastic. The bulbs simply pull out or are festoon-style that clip in.

Common Lighting Issues for this Generation

• Headlight Haze/Yellowing: Over time, the clear plastic headlight lenses can degrade, becoming cloudy or yellowed due to UV exposure. This significantly reduces light output. Restoration kits can help, but severe cases may require replacement housings.

• Tail Light Condensation: Some owners report moisture or condensation building up inside the taillight assemblies. This can be caused by a faulty seal or a crack in the housing. If left unaddressed, it can lead to premature bulb failure or wiring corrosion.

• Trailer Wiring Issues: F-350s often tow, and issues with trailer lighting (no lights, brake lights staying on, etc.) are common. Always check the truck's fuse box and trailer harness connections, as well as the trailer's wiring itself.

• LED Compatibility with Upgrades: As mentioned, attempting to upgrade incandescent bulbs to aftermarket LEDs without proper CANBUS decoders can lead to frustrating dash warnings and hyper-flashing. Ensure you use quality, compatible LED products.

• Loose Connections/Corrosion: Especially in trucks exposed to harsh weather or off-road conditions, electrical connections can become loose or corroded, leading to intermittent light operation. Inspect sockets and wiring harnesses if a bulb repeatedly fails or flickers.

Find a trusted shop on Repairius.