How to Replace Light Bulbs on a 2026 Harley-Davidson Fat Boy (FLFBS)

Harley-Davidson Fat Boy FLFBS · 2026 · Light Bulbs

Light Bulb Replacement Guide: 2026 Harley-Davidson Fat Boy FLFBS

This comprehensive guide covers every exterior light bulb position on the 2026 Harley-Davidson Fat Boy (FLFBS), including the headlight (low/high beam), front and rear turn signals, tail/brake light, running lights, and license plate light. The Fat Boy is a Softail model with its own distinct lighting setup — the iconic solid disc wheels, muscular fenders, and classic solo profile come with a lighting arrangement that differs from the Touring platform.

Quick Reference Bulb Table

Note: The 2026 Fat Boy uses an H4 (9003 / HB2) headlight bulb, which differs from the H13 used on the Touring models. The H4 is a common dual-filament bulb used in many motorcycles. Confirm your specific model year — some 2026 Fat Boy variants may be equipped with a Daymaker LED headlight from the factory, particularly higher trim levels.

Difficulty & Time Estimate

• Difficulty Level: Beginner to Intermediate (1 to 2 out of 5)
• Estimated Time: 30-60 minutes depending on positions replaced
• Best Done: In a well-lit area with the bike on a stand or level surface

Complete Tool List

OEM Part Numbers & Aftermarket Alternatives

Step-by-Step Instructions

Headlight (H4) — Low and High Beam

The 2026 Fat Boy uses an H4 (9003 / HB2) dual-filament halogen headlight bulb mounted in a 7-inch reflector behind the solo-style headlight nacelle. The H4 bulb is one of the most common motorcycle headlight bulbs and is widely available at auto parts stores.

Note: If your 2026 Fat Boy trim level came with the Harley-Davidson Daymaker LED Headlight, refer to the Daymaker replacement section below instead.

Step 1: Turn the ignition OFF and allow the headlight to cool for at least 10 minutes if the bike has been running.

Step 2: The Fat Boy headlight nacelle has a trim ring secured by three T-25 Torx bolts. Using a T-25 Torx driver, remove all three bolts and set them aside in a small container.

Step 3: Carefully pull the trim ring forward and set it on a clean, soft surface to prevent scratching the painted or chrome finish.

Step 4: You will now see the 7-inch reflector housing. Locate the electrical connector attached to the back of the H4 bulb.

Step 5: Press the release tab on the H4 connector and pull the connector straight off the bulb base. Do not pull on the wires — pull the plastic connector body.

Step 6: Remove the wire retainer clip or three-point mounting ring that holds the H4 bulb in place. If equipped with a wire retainer, press the clip inward and slide it sideways to release it from the bulb tabs. If equipped with a three-point screw ring, loosen the ring screws and rotate the ring clear.

Step 7: Gently pull the old H4 bulb straight out of the reflector housing by the base. Do not grip the glass barrel — skin oils on halogen glass create hot spots that cause premature bulb failure.

Step 8: Open the new H4 bulb and handle it by the metal base only. If you are using a halogen bulb, wear nitrile gloves. If you accidentally touch the glass barrel, clean it thoroughly with isopropyl alcohol and a lint-free cloth before installation.

Step 9: Insert the new H4 bulb into the reflector housing. The H4 has a three-tab base (one tab is slightly offset for correct orientation). Align the tabs with the housing slots and push firmly until the bulb is fully seated.

Step 10: Reinstall the wire retainer clip or mounting ring. The bulb should be firmly held in place with no wobble or movement.

Step 11: Reconnect the electrical connector, pushing firmly until it clicks into place.

Step 12: Before reinstalling the trim ring, turn the ignition ON and test the headlight. Verify the low beam illuminates, then switch to high beam and confirm both filaments are functioning correctly.

Step 13: Position the trim ring over the headlight and reinstall the three T-25 bolts. Tighten evenly — hand tight plus a gentle snug is sufficient. The trim ring is cosmetic and does not require high torque.

Step 14: Check and adjust the headlight beam aim (see the alignment procedure in the Tips section below).

Daymaker LED Headlight (If Equipped)

If your 2026 Fat Boy came with the Harley-Davidson Daymaker LED Headlight from the factory, there is no replaceable bulb inside the sealed LED assembly. If the headlight fails, the entire Daymaker unit must be replaced.

Step 1: Turn the ignition OFF and disconnect the battery negative terminal.

Step 2: Remove the T-25 trim ring bolts and set them aside.

Step 3: Disconnect the main electrical connector from the rear of the Daymaker assembly.

Step 4: Remove the Daymaker mounting bolts from the nacelle bracket.

Step 5: Carefully remove the entire Daymaker assembly and transfer any brackets to the replacement unit.

Step 6: Install the new Daymaker LED assembly, reconnect the electrical connector, and reinstall the trim ring.

Step 7: Reconnect the battery and test.

Front Turn Signals (1157NA) — Amber

The Fat Boy front turn signals are mounted on the lower triple tree / fork area in classic bullet-style amber housings.

Step 1: Turn the handlebars to the side that provides best access to the turn signal you are servicing. The Fat Boy's handlebar position usually provides good fork access without removing anything.

Step 2: Locate the rubber access grommet at the rear of the turn signal housing. Gently pull the grommet back to expose the bulb socket.

Step 3: Turn the bulb socket counterclockwise — approximately a quarter-turn — and pull the socket with the bulb straight out of the housing.

Step 4: Remove the old 1157NA amber bulb by pressing it gently into the bayonet socket and turning counterclockwise to unlock the two pins. Pull the bulb straight out.

Step 5: Insert the new 1157NA amber bulb into the socket. Align the two pins with the socket slots, push the bulb in, and turn clockwise until it locks into place. The bulb should not pull out when gently tugged.

Step 6: Before reassembly, turn the ignition on and activate the turn signal switch to verify the amber bulb is flashing correctly.

Step 7: Reinsert the socket and bulb assembly into the turn signal housing and turn clockwise to lock it in place.

Step 8: Reseat the rubber access grommet fully. Ensure it is seated all the way around the socket opening to keep moisture, road salt, and debris out of the housing.

Rear Turn Signals (1157NA) — Amber

Step 1: Access the rear turn signals mounted on the rear fender struts. The Fat Boy's wide, iconic fender provides reasonable access from the sides and rear.

Step 2: Locate the rubber access grommet at the rear of each turn signal housing and pull it back to expose the socket.

Step 3: Turn the socket counterclockwise and pull the socket with the bulb out.

Step 4: Remove the old 1157NA bulb: push in gently and turn counterclockwise to unlock.

Step 5: Install the new 1157NA amber bulb: push in and turn clockwise to lock.

Step 6: Test the turn signal from the handlebar switch before reassembly.

Step 7: Reinsert the socket into the housing and turn clockwise.

Step 8: Fully reseat the rubber access grommet.

Tail / Brake Light (1157) — Dual Contact

The Fat Boy tail light and brake light share a single 1157 dual-filament bulb mounted in the tail light housing beneath the rear fender. The filaments function as: - Dim filament: Tail light (running light, illuminates when ignition is on) - Bright filament: Brake light (activates when front brake lever or rear brake pedal is pressed)

Step 1: Locate the tail light housing mounted below the rear fender, typically integrated with the rear fender struts or mounted to a rear fender support bracket.

Step 2: Remove the one or two T-25 Torx screws that secure the tail light lens or housing to its mounting bracket. Some Fat Boy models may use Phillips screws — verify on your bike.

Step 3: Carefully pull the tail light lens/housing assembly away from the mounting bracket. On the Fat Boy, the rear fender width can make access slightly tight. You may need to angle the housing carefully.

Step 4: Identify the tail/brake bulb socket inside the housing (typically the center or largest socket).

Step 5: Turn the socket counterclockwise and remove it from the housing.

Step 6: Remove the old 1157 bulb by pressing it into the socket and turning counterclockwise to unlock.

Step 7: Install the new 1157 dual-contact bulb. Push into the socket and turn clockwise until it locks securely.

Step 8: Reinsert the socket into the tail light housing assembly and turn clockwise to lock.

Step 9: Test all three tail light functions before reinstalling the housing: - Turn ignition ON: the dim tail filament should illuminate - Squeeze the front brake lever: the bright brake filament should light up - Press the rear brake pedal: the bright brake filament should activate - Activate a turn signal: the appropriate side bulb should flash

Step 10: Reinstall the tail light housing/lens assembly and secure with the T-25 or Phillips screws.

Front Running Lights (1157)

The Fat Boy shares the front running light function with the front turn signal 1157 bulbs on most configurations. The dim filament of the 1157 serves as the running light (always on with ignition), and the bright filament activates during turn signal operation.

If your Fat Boy has separate nacelle/indicator running lights:

Step 1: Locate the indicator light housing(s) in the top of the headlight nacelle.

Step 2: Remove the retaining ring or unclip the housing.

Step 3: Pull the 194 wedge-base socket straight out (or turn the bayonet socket counterclockwise if equipped with bayonet).

Step 4: Replace the bulb (194 wedge or 1157 bayonet as appropriate).

Step 5: Reassemble and test with the ignition on.

License Plate Light (194 / W5W / T10)

Step 1: Locate the license plate light mounted near the rear fender license plate bracket. On the Fat Boy, this is typically on the top or side of the fender near the plate.

Step 2: Reach from beneath the rear fender to find the small wedge-based socket. The Fat Boy's wide fender may require reaching around the edge.

Step 3: Pull the socket straight out from the housing. Wedge-base bulbs do not twist — they are friction-fit.

Step 4: Pull the old 194 bulb straight out from the socket. Note the orientation of the two exposed wire contacts.

Step 5: Insert the new 194 bulb into the socket, ensuring the two wire contacts align with the terminal slots in the socket.

Step 6: Push the socket back into the housing, ensuring it seats firmly.

Step 7: Turn the ignition on and verify that the license plate is clearly illuminated. If the plate is not lit, recheck bulb seating and contact alignment.

Tips, Warnings & Common Mistakes

Headlight Alignment After Bulb or Assembly Replacement

Proper headlight beam alignment is critical for rider safety and legal compliance. Even though the Fat Boy has a single headlight (no fairing to complicate access), alignment must be checked:

1. Park the Fat Boy on level ground, exactly 25 feet from a flat wall or garage door. Ensure the bike is upright — use the side stand off a flat surface or have a helper steady the motorcycle.
2. Measure the vertical distance from the ground to the center of the headlight bulb/assembly.
3. Using painter's tape or chalk, draw a horizontal reference line on the wall at the measured height. Then draw a second horizontal line 2 inches below the first line.
4. Turn on the headlight low beam and observe the beam pattern on the wall.
5. The top edge of the bright zone (hotspot) should be at or slightly below the lower reference line. The beam should not be aimed upwards, which can blind oncoming drivers.
6. To adjust: Locate the headlight adjustment screws on the back and/or sides of the headlight housing. There is typically one screw for up/down adjustment and one for left/right adjustment.
7. Loosen the adjustment lock nut (if equipped), adjust the screw to aim the beam, and retighten the lock nut securely.
8. Re-verify the beam position on the wall.

LED vs. Halogen — Pros and Cons

LED Turn Signal Warning: If you replace the Fat Boy's incandescent 1157NA turn signal bulbs with lower-draw LED bulbs, the reduced circuit resistance can cause the flasher relay to trigger hyper-flashing (rapid blinking). Fix this by: - Installing load equalizer resistors included with most LED kits - Replacing the stock flasher relay with an LED-compatible module - Installing an electronic flasher module that auto-detects LED loads

Legal Notes

• All exterior lighting must comply with DOT/FMVSS 108 standards for use on public roads in the United States.
• Turn signals must emit amber light — clear bulbs behind amber lenses may be illegal in some states.
• LED headlight color temperatures above 6000K (blue-tint) are likely to fail vehicle inspection and may result in citations.
• If your state requires vehicle inspection, verify that any aftermarket LED headlight or assembly carries a DOT/FMVSS 108 marking.
• Aftermarket LED headlight assemblies (Daymaker replacements) must be specifically approved for H4-style mounting to be legal.

Common Mistakes to Avoid

Verification Notes for 2026 Model Year

The 2026 Fat Boy (FLFBS) continues the Softail platform with the Milwaukee-Eight engine. The following specifications should be verified against your owner's manual:

Because some 2026 Fat Boy trim levels may come with the factory Daymaker LED headlight, confirm whether your bike has the standard H4 halogen or the LED Daymaker assembly before purchasing replacement bulbs.

To verify all specifications, check your 2026 Fat Boy owner's manual included with the motorcycle, or access it through the Harley-Davidson mobile app.

This guide was prepared using Harley-Davidson OEM service manual specifications, OEM parts catalog data, and established industry bulb cross-references for the FLFBS Softail platform. Always verify against your specific owner's manual before performing maintenance.

Parts for this job

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