2018 Peterbilt 579 Bulb Size Guide

Quick Reference

The 2018 Peterbilt 579, a staple in the heavy-duty truck industry, offers a blend of classic ruggedness and modern amenities. When it comes to lighting, Peterbilt provided various options, meaning your 579 might have different bulb types depending on its original configuration and trim level. It's crucial to note whether your truck came equipped with traditional halogen lighting or the more advanced LED systems, as this significantly impacts replacement bulb choices.

For headlights, the 2018 579 typically features either halogen H11 for low beams and H9 for high beams, or a fully integrated LED headlight assembly. The LED option provides superior illumination and a longer lifespan, but if a module fails, it often requires replacing the entire headlight assembly rather than just a bulb. Fog lights commonly use an H10 halogen bulb, though LED fog light options were also available from the factory or as an aftermarket upgrade. Daytime Running Lights (DRLs) on the 2018 579 are almost exclusively LED, integrated into the headlight housing or a separate strip.

Turn signals, both front and rear, generally utilize incandescent 3157 or 7440 amber bulbs. Brake lights and tail lights often follow a similar pattern, with incandescent 3157/7443 red bulbs for brake lights and LED assemblies for tail lights on many configurations. Reverse lights typically use an incandescent 3157 or 7440 white bulb. Smaller exterior lights, such as license plate lights and side markers, commonly use smaller incandescent bulbs like the 194.

Interior lighting, including dome and map lights, typically relies on a variety of incandescent bulbs such as the 578, 906, or 194, depending on the specific fixture.

LED vs Halogen Upgrade Considerations

Upgrading from halogen to LED bulbs in your 2018 Peterbilt 579 can offer numerous benefits, including brighter light output, increased longevity, and a more modern appearance. However, there are important considerations, especially for a heavy-duty vehicle like the 579:

• CANBUS Errors: Modern vehicles, including the Peterbilt 579, use a Controller Area Network (CANBUS) system to monitor various electrical components. LED bulbs draw significantly less power than halogens, which can trick the CANBUS system into thinking a bulb is out, triggering dash warning lights. To prevent this, you'll often need CANBUS-compatible LED bulbs or load resistors/decoders for each LED bulb you install.
• Adapters and Fitment: While many aftermarket LED bulbs are designed to be "plug-and-play," some may require adapters or minor modifications to fit correctly into the existing bulb housing. Ensure the LED bulb's base matches the original halogen bulb's base.
• Beam Pattern: Some LED headlight conversions can create an improper beam pattern in halogen reflector housings, leading to glare for oncoming drivers and suboptimal light distribution. For the best results, consider LED bulbs specifically designed for reflector-style headlights or, ideally, an entire LED headlight assembly if upgrading from halogen headlights.
• Heat Dissipation: LEDs generate heat at their base, and proper heat dissipation is crucial for their longevity. Ensure there's adequate space for cooling fins or integrated fans on aftermarket LED bulbs.

How to Replace Each Bulb (Short Tips per Location)

• Low Beam/High Beam: Access is typically from behind the headlight assembly. For halogen bulbs, twist and pull the old bulb out, disconnect the electrical connector, and reverse the process. LED headlight assemblies usually require professional replacement.
• Fog Light: Often accessible from under the front bumper or by removing an access panel in the wheel well. Twist and remove the bulb, then disconnect the connector.
• DRL: Usually integrated into the headlight assembly. If a separate strip, access might be from the front or behind the bumper.
• Front Turn Signal: Often accessed by twisting out the bulb socket from the back of the turn signal housing, usually found in the bumper or fender fairing.
• Rear Turn Signal/Brake Light/Tail Light/Reverse Light: These are typically found in the rear tail light assembly. Access is generally from the rear of the truck; remove the lens screws or the entire housing to reach the bulb sockets. Twist out the bulb and replace.
• License Plate: Unscrew the lens cover (if applicable) or gently pry out the housing to access the bulb.
• Side Marker: These small bulbs are often accessed by gently prying off the lens or twisting out the socket from the back of the fixture.
• Dome/Map Light: Carefully pry off the clear lens cover to expose the bulb. Many of these are push-in or festoon-style bulbs.

Always disconnect battery power before performing any electrical work. Refer to your Peterbilt 579's owner's manual for specific instructions and diagrams relevant to your truck's configuration.

Common Lighting Issues for this Generation

The 2018 Peterbilt 579 is generally a reliable truck, but like any vehicle, some common lighting issues can arise:

• Bulb Burnout: Incandescent bulbs simply burn out over time. This is the most common issue. Keep spare bulbs on hand, especially for critical lighting like headlights and brake lights.
• Corroded Sockets/Connectors: Exposure to road salt, moisture, and general wear and tear can lead to corrosion in bulb sockets and electrical connectors, causing intermittent or complete bulb failure. Cleaning with electrical contact cleaner or replacing the socket may be necessary.
• Trailer Wiring Issues: Given the 579's role as a tractor, issues with trailer wiring harnesses are frequent. Faulty trailer connections or shorts can cause issues with the truck's tail lights, brake lights, and turn signals, often leading to "bulb out" warnings on the dash.
• DRL Malfunctions (LED): While durable, integrated LED DRLs can sometimes have individual diodes fail over time, resulting in a partial or non-functioning light strip. Repair often means replacing the entire DRL module or headlight assembly.
• Headlight Condensation: Seals around headlight assemblies can degrade, allowing moisture to enter and cause condensation. While not directly a bulb issue, it can obscure light output and accelerate bulb failure. Sealing the assembly or replacing it may be required.

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