Turn Signal Bulb - Rear

This procedure covers the replacement of the rear turn signal bulb on a 2011-2014 Ford F-150 3.5L EcoBoost 4WD by accessing the taillight assembly from inside the bed or by removing the taillight housing.

Warnings

Tools required

Parts

• Rear turn signal bulb (3157A or 3157 amber) × 1 — Sylvania 3157A or equivalent

Preparation

1. Park vehicle on level surface and turn off ignition
2. Allow taillight bulbs to cool if vehicle was recently operated
3. Identify which side (driver or passenger) requires bulb replacement
4. Lower tailgate for better access to taillight assembly

Procedure

1. 1

   Access the taillight assembly
   From inside the bed, locate the two plastic wing nuts or fasteners securing the taillight assembly to the body. These are accessed from the rear corner of the bed, behind the taillight location. If bed liner is installed, you may need to pull it back slightly for access.
2. 2

   Remove taillight assembly fasteners
   Turn both plastic wing nuts counterclockwise by hand to remove them. Keep these fasteners in a safe location as they are easily lost. The taillight assembly should now be loose but still connected by the wiring harness.
3. 3

   Pull taillight assembly rearward
   Carefully pull the entire taillight assembly straight back away from the vehicle body. The assembly slides rearward on locating pins. Pull gently to avoid damaging the wiring harness or connectors. You only need to pull it back 3-4 inches to access the bulb sockets.
4. 4

   Identify and remove turn signal bulb socket
   Locate the turn signal bulb socket on the back of the taillight assembly. The turn signal is typically the amber/orange lens position. Grasp the bulb socket and rotate it counterclockwise approximately 1/4 turn, then pull it straight out of the housing.
5. 5

   Remove failed bulb
   The 3157 bulb is a bayonet-style dual-filament bulb. Press the bulb gently into the socket while rotating counterclockwise about 1/4 turn to release the bayonet pins, then pull the bulb straight out. Inspect the socket for any corrosion, melting, or damage.
6. 6

   Install new turn signal bulb
   Insert the new 3157A amber bulb into the socket, aligning the offset bayonet pins with the socket slots. Press in gently and rotate clockwise 1/4 turn until it locks into place. Do not touch the glass portion of the bulb with bare fingers as oils can cause premature failure.
7. 7

   Test bulb operation
   Before reinstalling the socket, have an assistant turn on the ignition and activate the turn signal for the side being serviced. Verify the bulb illuminates properly for both the turn signal function and hazard function. If bulb does not illuminate, check socket connection and bulb installation.
8. 8

   Reinstall bulb socket
   Insert the bulb socket back into the taillight housing, aligning the tabs with the slots. Push in and rotate clockwise 1/4 turn until it locks securely. Ensure the socket is fully seated and locked.
9. 9

   Reinstall taillight assembly
   Carefully push the taillight assembly forward onto the body locating pins, ensuring proper alignment. The assembly should slide smoothly into position and seat flush against the body panel gasket.
10. 10

    Secure taillight assembly
    From inside the bed, thread both plastic wing nuts clockwise by hand onto their mounting studs. Tighten firmly by hand only - do not use tools as overtightening can crack the housing. Ensure the assembly is snug and does not rattle.

Reassembly

1. Ensure taillight assembly gasket is properly seated to prevent water intrusion
2. Reposition bed liner if it was moved during access

Verification

• Turn ignition to ON position and activate turn signals to verify proper operation
• Test hazard lights to confirm bulb functions in both modes
• Visually inspect taillight assembly to ensure it is flush and properly aligned with body panels
• Verify no gap exists between taillight housing and body that could allow water or debris entry

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