Kenworth T680 Headlight Bulb Size & Replacement Guide

Everything you need to know about Kenworth T680 headlight bulbs — including bulb sizes, LED upgrades, assembly replacement, and wiring basics.

Kenworth T680 Headlight Bulb Size

The Kenworth T680 has been in production since 2013, and Kenworth has used a few different headlight configurations depending on the model year and trim. Here's what you need to know:

2013–2021 Kenworth T680 Headlight Bulbs

• Low Beam: H11 halogen (55W)
• High Beam: 9005 (HB3) halogen (65W)
• Turn Signal: 3157A amber
• Parking / Marker Light: 194 / T10 wedge
• Daytime Running Light (DRL): Varies — some trims use the low beam circuit, others have a dedicated LED strip

2022+ Kenworth T680 (Next Gen)

• Low Beam: H11 (halogen or factory LED depending on trim)
• High Beam: 9005 (HB3)
• DRL: Integrated LED (non-replaceable strip in most configurations)
• Turn Signal: 7440A amber

Note: The T680 has had multiple headlight housing designs. Always cross-reference your VIN and check your existing bulb before ordering.

Kenworth T680 Headlight Bulb Type: Halogen vs. LED

The factory T680 comes with halogen bulbs in most configurations. If you're wondering whether to stick with halogen or upgrade to LED, here's the comparison:

Halogen (Stock)

• Warm yellowish light (~3200K color temperature)
• ~1,000 hour bulb lifespan
• Cheap to replace ($10-25 per bulb)
• Lower light output compared to LED

LED Upgrade

• Bright white light (6000K-6500K)
• 50,000+ hour lifespan — essentially the life of the truck
• 200-300% brighter than halogen
• Lower power draw (35W vs. 55W for low beam)
• Better visibility in rain, fog, and dark rural highways

What to Look for in T680 LED Bulbs

Not all LED bulbs are created equal. For the T680 specifically, look for:

Proper beam pattern — The bulb needs to replicate the halogen filament position so the reflector housing aims the light correctly. Cheap LEDs scatter light everywhere and blind oncoming traffic without actually improving your visibility.

Active cooling — Built-in fans or braided copper heat sinks. The T680 headlight housing doesn't have a ton of airflow, so passive-only cooling can overheat and cause premature failure.

Canbus compatible — Some LED bulbs trigger "bulb out" warnings on the T680 dash. Look for bulbs with built-in resistors or Canbus-ready drivers to avoid phantom error codes.

Correct fitment — H11 for low beam, 9005 for high beam. Make sure the base locks into your existing socket without modification. If you have to force it, it's the wrong bulb.

When to Replace the Kenworth T680 Headlight Assembly

Sometimes a bulb swap isn't enough. Here are the signs that the entire headlight assembly needs replacement:

Moisture trapped inside the housing — Water intrusion means the seal is compromised. You'll see condensation on the inside of the lens, especially after rain or truck washes. Once moisture gets in, it corrodes the reflector coating and socket contacts. Silicone sealant is a temporary fix, but the damage is usually progressive.

Cracked or broken lens — Road debris, parking lot contact, or minor collisions can crack the polycarbonate lens. Even a small crack lets water, dust, and road salt into the housing.

Yellowed or hazed lens — Years of UV exposure turn the clear lens cloudy and yellow. This scatters the beam pattern and cuts your effective visibility distance significantly. Restoration kits help temporarily, but they wear off within 6-12 months on a truck that lives outside.

Corroded or melted connectors — If the bulb socket is corroded, melted, or showing signs of heat damage, the wiring inside the assembly is compromised. Replacing just the bulb will lead to the same failure. A new assembly with fresh connectors solves the root cause.

Failed chrome reflector — The reflective coating inside the housing degrades over time, especially with moisture exposure. If your headlights seem dim even with new bulbs, the reflector may be the problem.

Kenworth T680 Headlight Assembly: OEM vs. Aftermarket

OEM Kenworth headlight assemblies from the dealer typically run $1,000–$2,000+ per side depending on the configuration. For a working truck, that's a significant expense on top of downtime.

Quality aftermarket assemblies provide the same fitment and performance at a fraction of the cost:

• Direct bolt-on replacement — same mounting points as OEM
• DOT/SAE compliant lenses with proper beam patterns
• UV-resistant polycarbonate lens coating
• OEM-spec electrical connectors for plug-and-play installation
• Available in chrome or black housing options

At EverTrust Parts, our Kenworth T680 headlight assemblies are built to match OEM specifications. Direct-fit, no modifications needed.

How to Replace Kenworth T680 Headlights: Step by Step

Tools You'll Need

• 10mm socket and ratchet
• 13mm socket (some model years)
• T30 Torx bit
• Phillips head screwdriver
• Flat-head screwdriver or trim removal tool
• Clean microfiber cloth
• Electrical contact cleaner

Headlight Assembly Replacement

Step 1: Preparation. Park on a flat surface and make sure the truck is off. Open the hood and identify the headlight assembly mounting points. The T680 typically has 3-4 mounting bolts accessible from the top and side of the assembly.

Step 2: Disconnect the electrical harness. Locate the wiring connector behind the headlight assembly. Press the release tab firmly and pull the connector straight back. Don't twist or pry — these connectors are designed to release with a straight pull once the tab is depressed.

Step 3: Remove the mounting bolts. Using a 10mm socket (13mm on some years), remove the bolts holding the assembly in place. There are usually two on top and one or two on the inner side. Keep one hand on the assembly as you remove the last bolt so it doesn't drop.

Step 4: Remove the assembly. Pull the headlight assembly straight forward and out. On some T680 models, you may need to gently wiggle it to clear the fender alignment pins. If it's stuck, check for any hidden clips or brackets you may have missed.

Step 5: Transfer components if needed. If your new assembly doesn't include bulbs, transfer them from the old unit. This is also a good time to upgrade to LED bulbs if you've been planning to.

Step 6: Install the new assembly. Set the new headlight into position, making sure the alignment pins seat properly. Start all mounting bolts by hand first, then tighten them evenly. Don't overtighten — you can crack the mounting tabs.

Step 7: Reconnect the electrical harness. Push the connector in until it clicks. Give it a gentle tug to confirm it's locked.

Step 8: Test all functions. Turn on the headlights and verify: low beam, high beam, turn signal, parking light, and DRL (if equipped). Check both sides to make sure everything is working.

Step 9: Aim the headlights. Park 25 feet from a flat wall. The hot spot of each beam should be slightly below the horizontal centerline and slightly to the right. Use the built-in adjustment screws on the back of the assembly to dial in the aim.

Kenworth T680 Headlight Wiring Diagram Basics

If you're troubleshooting electrical issues rather than replacing the whole assembly, here's what you need to know about the T680 headlight circuit:

Power source: The headlight circuit is fed from the fuse panel on the driver's side dash. Low beams and high beams run on separate circuits with separate fuses (typically 15A and 20A respectively).

Switching: The headlight switch on the dash sends a signal to the body controller module (BCM), which activates the appropriate relay to power the headlights. If your headlights aren't working at all, the issue could be the switch, the BCM, or the relay — not just the bulb.

Ground path: Each headlight assembly has its own ground wire that connects to a chassis ground point near the fender. Corroded or loose grounds are one of the most common causes of dim or flickering headlights on the T680.

Common wiring issues:

• Corroded ground connections — clean the ground point and connector with sandpaper and contact cleaner
• Chafed wiring near the fender where the harness passes through — inspect for bare wire and repair with heat-shrink connectors
• Melted connector pins from running halogen bulbs with corroded contacts — the increased resistance generates heat. Replace the connector and clean the contacts before installing new bulbs.

Pro tip: If you're having intermittent headlight problems, start with the grounds. Nine times out of ten, it's a ground issue.

Common Kenworth T680 Headlight Problems

Headlights dim at idle, bright when driving: This is almost always an alternator or charging system issue. Check your battery voltage at idle — it should be 13.5-14.5V. Below that, the alternator isn't keeping up and the headlights dim because they're running on battery voltage alone.

One side brighter than the other: Swap the bulbs side to side. If the dim side follows the bulb, replace the bulb. If it stays on the same side, you have a wiring or ground issue on that side.

Headlights flicker over bumps: Loose connector, worn socket, or a ground wire that's barely making contact. Wiggle the connector with the lights on — if it flickers, you've found the problem.

Turn signals work but headlights don't: Separate circuits. Check the headlight fuse first, then the headlight relay, then the switch. The turn signal circuit is independent from the headlight circuit.

LED bulbs causing "bulb out" warning: The T680's BCM monitors current draw. LED bulbs draw less current than halogen, so the truck thinks the bulb is burned out. Install LED-specific resistors or use Canbus-compatible LED bulbs to solve this.

Shop Kenworth T680 Headlights at EverTrust Parts

We carry aftermarket headlight assemblies for the Kenworth T680, plus headlights and parts for Freightliner, Peterbilt, Hino, Isuzu, and more.

Why truck owners choose EverTrust:

• OEM-quality fitment at aftermarket prices
• Fast shipping across North America (USA & Canada)
• Real truck parts expertise — we know these trucks

Browse Kenworth Headlights →

Need help finding the right headlight for your T680? Contact us at sales@evertrustparts.com and include your truck's year and VIN — we'll match you with the right part.

Related Guides

• Cross-Reference Part Number Guide
• Complete Buying Guide
• Cascadia Fitment Guide
• T680/T880 Compatibility Guide

Related: Peterbilt 389 grille assembly | Peterbilt 389 headlight housing