2017-2020 Ford F-150 Headlight Side Marker: Bulb vs. Full Assembly Replacement

Understanding Your F-150's Side Marker Light: Halogen vs. LED

For the 2017-2020 Ford F-150, the front side marker light is not a separate part you can buy on its own. It is built into the headlight assembly. The most important thing to know is which type of headlight your truck has, as this determines how the side marker is serviced.

• Halogen Headlights: Found on XL, XLT, and some Lariat trims, these assemblies use a small, replaceable incandescent bulb for the side marker function. The bulb is typically a 194 or 3157 type. If the side marker is out, you only need to replace this inexpensive bulb.
🎬 Watch: Quick and easy halogen bulb replacement walkthrough.
• LED Headlights: Standard on higher trims like Lariat (502A), King Ranch, Platinum, and Limited, these assemblies feature a signature C-shaped daytime running light. The amber side marker is a bank of integrated, non-serviceable LEDs. If these LEDs fail, the entire headlight assembly must be replaced.

Most Common Symptoms of Failure

Diagnosing a side marker issue is usually straightforward. Here’s what to look for:

• Side Marker Light is Out: The most obvious symptom. On halogen units, this means a burned-out bulb. On LED units, it signifies a failure of the internal LED module.
• Flickering Light (LED models): Before failing completely, the integrated LEDs in the high-end headlights may flicker. This is often a sign of moisture inside the housing causing a short.
• Condensation or Water Inside Headlight: This is a very common issue. While Ford states that minor fogging that clears on its own can be normal due to the vented design, any visible water droplets, streaks, or puddling indicates a failed seal. This moisture is a primary cause 🎬 See how to remove moisture and water from your headlights. of failure for both halogen bulb sockets (corrosion) and LED modules (short circuits).

Known Issues, Recalls, and TSBs

There is one major recall that affects the LED headlight units on these trucks.

Recall 20C03 / NHTSA Campaign 20V193000

This recall applies to 2018-2020 Ford F-150s equipped with factory LED headlamps. The issue is that when the headlight switch is manually turned on, the daytime running lamps (DRLs) may not dim as required by law, creating excessive glare for oncoming drivers. Ford dealers perform a free software update to the Body Control Module (BCM) to correct this. While this doesn't directly affect the side marker, it's a critical issue for any owner of an F-150 with LED headlights.

Buying a Used Side Marker Light (Headlight Assembly)

Since the side marker is part of the headlight, you are actually shopping for a complete headlight assembly. Given the extremely high cost of new OEM LED units, a used assembly is an excellent value. Here’s what to check:

• Verify the Technology (Halogen vs. LED): This is the most critical step. A halogen assembly will not work on a truck wired for LEDs, and vice-versa, without extensive modification. Halogen units have round dust caps for bulb access, while LED units have large metal heat sinks and complex wiring connectors. Match the part number from your old headlight exactly.
• Inspect for Cracks and Seals: Carefully examine the lens for any cracks or deep scuffs. More importantly, check the seal where the clear lens meets the black plastic housing. Any sign of separation or damage means it will leak.
• Check All Mounting Tabs: The headlight assembly is held in by several plastic tabs. These are brittle and often break during removal or in minor accidents. Ensure all tabs are present and intact. A headlight with broken tabs will vibrate or sit crooked.
• Look for Signs of Moisture: Check for a 'water line,' mineral deposits, or a hazy film on the inside of the lens. This indicates it has leaked in the past and the internal electronics (especially on LED models) may be compromised.
• For LED Assemblies, Test if Possible: If buying from a local seller, ask if they can connect it to a 12V power source to test the LED functions, including the amber side marker.

Cost Breakdown

The cost difference between servicing a halogen unit and an LED unit is massive.

Replacement Guide

Halogen Side Marker Bulb Replacement (Difficulty: 2/5)

Replacing the side marker bulb does not require removing the headlight assembly, but it is in a tight spot.

1. Turn the steering wheel to move the front tire out of the way.
2. Remove the screws holding the front edge of the plastic wheel well liner.
3. Peel the liner back to gain access to the back of the headlight assembly.
4. Locate the side marker bulb holder. It's often a long, gray or black plastic socket. Forum users note the passenger side is significantly harder to reach due to the placement of other components.
5. Twist the holder counter-clockwise and pull it out of the housing.
6. Pull the old bulb straight out of the socket and insert the new one. It's a good practice to wear gloves to avoid getting skin oils on the new bulb.
7. Test the light before reassembling.
8. Insert the socket back into the housing, twist clockwise to lock it, and secure the wheel liner.

LED Headlight Assembly Replacement (Difficulty: 3/5)

If your LED side marker has failed, the entire assembly must be replaced. This is a bolt-on procedure but requires removing trim.

1. Open the hood.
2. Remove the plastic trim pieces surrounding the grille and on top of the headlight.
3. Unbolt the grille and carefully pull it forward to access the bolts for the headlight assembly.
4. Remove the bolts securing the headlight assembly to the truck frame.
5. Carefully pull the assembly forward and disconnect the main electrical harness on the back.
6. Install the new assembly by reversing the process. Ensure the new headlight is properly aligned to avoid blinding other drivers.

Frequently Asked Questions