Peterbilt 579 Headlight Bulb Size & Assembly Replacement Guide

Complete guide to Peterbilt 579 headlight bulbs — bulb sizes by year, assembly replacement steps, LED upgrades, and troubleshooting common headlight issues.

Peterbilt 579 Headlight Bulb Size

The Peterbilt 579 has been a flagship highway tractor since its 2012 launch. Headlight specifications vary depending on model year and whether you have the original design or the 2019+ facelift.

2012–2020 Peterbilt 579 (Original Design)

• Low Beam: H11 halogen (55W)
• High Beam: 9005 (HB3) halogen (65W)
• Turn Signal: 3157A amber
• Parking / Marker Light: 194 / T10 wedge

2021–2025 Peterbilt 579 (New Model / Ultraloft)

• Low Beam: H11 (halogen standard, LED available on higher trims)
• High Beam: 9005 (HB3)
• Daytime Running Light: Integrated LED light bar (non-serviceable)
• Turn Signal: 7440A amber

The 2019+ models have a redesigned front end with a more aerodynamic headlight shape. The housings are NOT interchangeable between the pre-facelift and post-facelift 579.

Always confirm with your VIN before ordering. Peterbilt trim packages affect which headlight configuration your truck has.

Peterbilt 579 Headlight Assembly: When to Replace

A bulb swap is the cheapest fix, but sometimes the entire headlight assembly is the problem. Here's when replacement makes sense:

Water inside the housing — If you see condensation or pooled water behind the lens, the seal has failed. Moisture corrodes the reflector coating, eats the bulb socket contacts, and can short out wiring. Temporary fixes like drilling drain holes or applying RTV sealant usually just delay the inevitable.

Clouded, yellowed, or pitted lens — The polycarbonate lens takes a beating from UV, road salt, and debris. A severely degraded lens can cut your effective light output by 40-60%. Professional restoration is possible but usually only lasts 6-12 months on a truck that runs year-round.

Cracked housing or lens — Any crack is an entry point for water and contamination. A cracked headlight will also fail DOT inspection in most states and provinces.

Delaminated reflector — The chrome reflector coating inside the housing peels or flakes off over time, especially with heat cycling and moisture exposure. There's no repair for this — the whole assembly needs to go.

Repeated bulb failures — If you're going through bulbs every few months, the socket or wiring inside the assembly is likely causing excessive heat or voltage spikes. A new assembly with clean connectors solves the root cause.

OEM vs. Aftermarket Peterbilt 579 Headlights

OEM Peterbilt headlight assemblies from the dealer run $1,200–$2,500+ per side depending on year and configuration. The post-2019 assemblies with integrated LED DRLs are on the higher end.

Quality aftermarket headlight assemblies offer the same fit and function:

• Bolt-on replacement with OEM mounting points
• DOT/SAE compliant lens and beam pattern
• UV-coated polycarbonate lens
• Pre-wired connectors that match the factory harness
• Chrome or black housing options available

The key is choosing a reputable aftermarket supplier that builds to OEM specs. Cheap generic housings often have poor beam patterns that scatter light instead of focusing it, and thin lens coatings that yellow within a year.

EverTrust Parts carries aftermarket Peterbilt 579 headlight assemblies built to OEM specifications — direct fit, no modifications, ships fast.

How to Replace Peterbilt 579 Headlights: Step by Step

Tools You'll Need

• 10mm socket and ratchet
• T30 Torx bit (some model years)
• Flat-head screwdriver or trim tool
• Phillips head screwdriver
• Electrical contact cleaner
• Clean microfiber cloth
• Zip ties (to re-secure wiring)

Step-by-Step Replacement

Step 1: Access the headlight. Open the hood. The Peterbilt 579 headlight assembly is accessible from the engine bay side. Identify the mounting bolts — typically 3 bolts: two on top, one on the inner side.

Step 2: Disconnect electrical connectors. There are usually 2-3 connectors per headlight assembly (main harness, turn signal, DRL if equipped). Press the release tab on each connector and pull straight back. Label or photograph the connectors if you're concerned about getting them mixed up during reinstall.

Step 3: Remove the mounting bolts. Use a 10mm socket for the mounting bolts. On the 2019+ 579, there may also be a Torx bolt on the lower bracket. Support the assembly as you remove the final bolt.

Step 4: Pull the assembly forward. Gently slide the headlight assembly straight forward. The 579 uses alignment pins on the back of the housing that seat into grommets on the body — it should slide out smoothly once the bolts are removed. If it feels stuck, double-check for any clips you may have missed along the bottom edge.

Step 5: Prepare the new assembly. If your replacement assembly doesn't come with bulbs, transfer them from the old unit. Inspect the bulbs while they're out — if the filament looks thin or the glass is darkened, replace them now rather than pulling the assembly again later. Clean the bulb base and socket with contact cleaner.

Step 6: Install the new assembly. Align the mounting pins and slide the new headlight into position. Start all bolts by hand before tightening. Snug them evenly — don't crank one bolt tight while the others are loose, or you can stress the housing tabs.

Step 7: Reconnect all electrical connectors. Push each connector in until it clicks. Tug gently to verify the lock is engaged. Secure any loose wiring with zip ties to keep harnesses away from hot engine components.

Step 8: Test everything. Key on, engine off — check low beam, high beam, turn signal, parking light, and DRL. Walk around and verify both sides. Turn on the hazards to check the blink rate (a fast blink rate means a bulb is out or a connector isn't seated).

Step 9: Aim the headlights. Park 25 feet from a flat, light-colored wall. Each beam's hot spot should sit slightly below horizontal center and slightly to the right. The 579 has adjustment screws accessible from the rear of the headlight housing.

LED Headlight Upgrades for Peterbilt 579

Switching from halogen to LED is one of the most popular upgrades for the 579. Here's what the upgrade gets you:

• Significantly brighter output — LED H11 bulbs put out 2-4x the lumens of stock halogen
• Whiter light — 6000-6500K color temperature vs. the yellowish 3200K of halogen. Whiter light shows better contrast on road markings, signs, and obstacles
• Longer lifespan — 50,000+ hours vs. about 1,000 hours for halogen. With typical truck usage, LED bulbs can last the life of the truck
• Lower power draw — LED draws about 35W vs. 55W for halogen on the low beam circuit. Less draw means less heat in the connector and less load on the alternator

LED Installation Tips for the 579

The H11 and 9005 sockets in the 579 headlight housing have limited depth behind the assembly. When choosing LED bulbs, measure the space behind the headlight to make sure the bulb's driver and heat sink fit without hitting the dust cap or fender wall.

Some LED bulbs require you to remove the rubber dust cap on the back of the housing and use a larger cap or leave it off. If you run without a dust cap, debris and moisture can get into the housing. Look for LED bulbs that are compact enough to work with the stock dust cap, or buy replacement silicone dust caps that accommodate the larger LED base.

Common Peterbilt 579 Headlight Problems & Fixes

One headlight out, other works fine: Start with the obvious — check the bulb. Then check the fuse. Low beam and high beam are on separate fuses. If the bulb and fuse are good, check the connector at the headlight for corrosion or a loose fit.

Both headlights dim: Check your alternator output. At idle with accessories on, you should see 13.5-14.5V at the batteries. If voltage is low, the headlights dim because they're effectively running on battery power alone. Also check both headlight ground connections.

Headlights flicker: Usually a loose connection or bad ground. With the lights on, wiggle the connector at the headlight. If the light flickers, the connector needs cleaning or replacement. Also check the ground wire connection — clean it with sandpaper and retighten.

Condensation inside new headlights: A small amount of condensation after washing or driving in rain is normal for any headlight — the housing breathes through vent tubes. It should clear within 30-60 minutes of driving with the lights on. If condensation persists or you see standing water, check that all vent tubes are clear and all seals are properly seated.

Headlights won't turn off: Usually a stuck headlight relay or a faulty headlight switch. Check the relay first — it's in the fuse panel and can be swapped with an identical relay from another circuit to test.

Shop Peterbilt 579 Headlights at EverTrust Parts

We stock aftermarket headlight assemblies for the Peterbilt 579 (2012–2025), along with headlights and body parts for Freightliner, Kenworth, 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 Peterbilt Parts →

Need help finding the right headlight for your 579? Contact us at sales@evertrustparts.com with your truck's year and VIN — we'll match you with the exact part.

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