Buy Ford Focus Brake Light Bulbs

Your Ford Focus's brake light bulb-also known as the stop-lamp, tail-lamp, or rear brake lamp-plays a big role in letting drivers behind you know when you slow down. Most Focus models built between 2000 and 2018 use a dual-filament 3157 miniature bulb that serves as both a dim running light and a bright brake signal, while many European versions from the same years use a P21/5W or W21/5W equivalent. (AUXITO, focusfanatics.com) A healthy bulb shines red, draws roughly 26.9 watts on the brake circuit, and produces about 400 lumens-bright enough to meet federal rules that require a steady, red warning light. (oreillyauto.com, ecfr.gov)

• Common sizes by year
  • 2000-2007 (sedan & hatch): 3157 or 3156 dual-filament. (AUXITO)
  • 2008-2011: 3157 for outer stop-lamps; high-mount uses T10/2825. (focusfanatics.com)
  • 2012-2018 (Mk 3): 3157 for main cluster; center lamp uses W5W. (YouTube, YouTube)
  • Always check your owner's manual before you buy, because trim-level or country can change the socket code. (focusfanatics.com)
• Electrical specs
  • Voltage: 12.8 V nominal, 14 V charging. (oreillyauto.com)
  • Wattage: 8.3 W (tail) / 26.9 W (brake).
  • Base type: W2.5 × 16q (plastic wedge). (AutoZone.com)
• Filament vs LED-LEDs switch on about 0.2 seconds faster than filaments. That tiny gap can trim nearly 15 feet of stopping distance if the car behind you is traveling 50 mph, according to a U.S. study on LED stop-lamps. (crashstats.nhtsa.dot.gov)

A quick rule of thumb: if your Focus uses a dual-filament bulb for both tail and brake functions, the replacement code will almost always read Ò3157, 3157LL, or 3157K.Ó European-market Focus cars that label the socket ÒP21/5WÓ or ÒW21/5WÓ accept the same physical dimensions, just under a different naming system. (AUXITO, webcdn.intercars.eu) Mixing codes (for example, putting a single-filament 3156 into a dual-filament socket) will leave you with either no brake light or no tail light. (Reddit)

• In the United States, Federal Motor Vehicle Safety Standard 108 requires every brake lamp-including the high-mounted light-to emit a steady red beam when you press the pedal. Pulsing or color-changing kits violate that rule. (ecfr.gov, NHTSA)
• UK drivers must keep all rear lights working from sunset to sunrise, per Rule 113 of the Highway Code, and any lamp that fails will lead to an MOT test failure because stop-lamps must glow a constant red. (THE HIGHWAY CODE, gov.uk)
• A corroded rubber bumper in the pedal assembly once triggered a Ford recall because stuck brake lights could confuse following traffic. (autobodynews.com)

For more details, see the official text of FMVSS 108 on the eCFR site and the UK's MOT Inspection Manual.

• Dark lens: No red glow when a helper presses the pedal. (YouTube)
• Warning chime or message: Some trim levels flag a bulb-out. (YouTube)
• Fast-flashing indicators (Òhyper-flashÓ): Happens if you fit LED bulbs without a load resistor. (YouTube)
• Intermittent outage: Vibrations or moisture shorten filament life; LEDs handle these better. (The Spruce, Car Talk Community)

1. Open the hatch and remove the two Torx-head screws holding the rear lamp assembly. (YouTube)
2. Slide the cluster straight back to clear the locator pins.
3. Twist the bulb socket counter-clockwise and pull it out.
4. Grip the old bulb, rock it gently, and lift. Wear gloves to avoid oil on the glass. (YouTube)
5. Push the new bulb firmly into the socket, align the tabs, and twist to lock.
6. Reinstall the lamp, test with a friend behind the car, then check the high-mount light.

If both sides stay dark, check the 10-amp stop-lamp fuse in the passenger-compartment fuse box; the slot numbers vary by model year. (YouTube)

Upgrading to an LED brake bulb can last up to 25,000-30,000 hours-hundreds of times longer than a 100-hour incandescent rating. (yourmechanic.com, oreillyauto.com) LED chips also run cooler and draw less current, which helps your Focus's alternator. Drivers on enthusiast forums note a clearer, faster Òinstant-onÓ look that stands out in rain or fog. (NSX Prime) Make sure any LED you install is marked ÒDOTÓ or ÒE-markÓ so it meets road-legal brightness levels. (crashstats.nhtsa.dot.gov, webcdn.intercars.eu)

• Clean dust off the red lens-dirt can cut brightness by 20 percent. (The Spruce)
• Replace bulbs in pairs so brightness matches left and right. (Car Talk Community)
• Keep a spare 3157 bulb and a T25 Torx driver in the trunk for emergencies.
• Test your brake lights monthly by reversing toward a garage door or wall; you'll see the reflection. (THE HIGHWAY CODE)

• Touching the glass of a halogen bulb-fingerprints cause hot spots that shorten life. (The Spruce)
• Mixing single- and dual-filament bulbs. (Reddit)
• Skipping the load resistor when switching to LED (causes hyper-flash). (YouTube)
• Forgetting the high-mounted lamp-law requires all stop-lamps to work. (ecfr.gov)

• U.S. FMVSS 108 text (lamp regulations) via the eCFR website.
• NHTSA interpretation on steady-burning third brake lights: Official letter.
• Research report on LED stop-lamp effectiveness (PDF): NHTSA CrashStats.
• UK lighting rules: Highway Code Rule 113.
• MOT stop-lamp standards: GOV.UK manual.
• Detailed DIY video: Change the Tail Lights on a Ford Focus.
• Community discussion on Focus bulb sizes: FocusFanatics thread.
• Tips on bulb life and failures: The Spruce article.

With the right bulb size, steady red glow, and a few easy checks, your Ford Focus will signal stops clearly and stay road-legal.