2020 Peterbilt 579 Bulb Size Guide

Quick Reference Bulb Size Chart: 2020 Peterbilt 579

Note: Some 579 models came equipped from the factory with full LED lighting assemblies. These are sealed units and individual bulbs cannot be replaced. The entire headlight or tail light housing must be replaced if a failure occurs.

LED vs. Halogen Upgrade Considerations

Upgrading your 2020 Peterbilt 579 from standard halogen/incandescent bulbs to LEDs is a popular choice for improving visibility and modernizing the truck's appearance. However, there are a few key things to keep in mind before you make the switch.

• CANBUS Errors: The 579's computer system (CANBUS) monitors the electrical current drawn by the lighting circuits. Since LEDs draw significantly less power than halogen bulbs, the system can misinterpret this as a "bulb out" error, leading to a persistent warning light on your dashboard. To fix this, you will need to install "CANBUS-ready" LED bulbs or add an inline resistor to the circuit for each bulb you replace. This mimics the electrical load of the original halogen bulb.
• Headlight Adapters & Beam Pattern: When upgrading H11 or 9005 halogen headlight bulbs to LED, the physical fit is usually straightforward. However, the most critical factor is achieving the correct beam pattern. Poorly designed LED bulbs can scatter light, blinding oncoming drivers and failing to illuminate the road effectively. Look for high-quality, adjustable LED bulbs that allow you to rotate the bulb in the housing to mimic the original halogen filament's position. This is crucial for maintaining a safe and legal beam pattern in the factory reflector or projector housings.
• Color Temperature: LED bulbs come in a range of color temperatures, measured in Kelvin (K). A 5000K to 6000K bulb will produce a crisp, pure white light that is much brighter and clearer than the yellowish tint of a standard halogen bulb (around 3200K).

How to Replace Each Bulb

Replacing bulbs on the 579 is generally straightforward with basic hand tools.

• Headlights & Fog Lights: Access is gained by opening the hood. The bulb sockets are at the back of the headlight and fog light assemblies. Twist the socket counter-clockwise to remove it, replace the bulb, and reinstall. Wear gloves to avoid touching the glass of new halogen bulbs, as oils from your skin can cause them to fail prematurely.
• Front Turn Signals: These are also located within the main headlight assembly and can be accessed similarly from behind the housing under the hood.
• Tail Lights, Brake, & Reverse Lights: The rear combination lamps are held to the cab or sleeper fairings by a few screws (usually Phillips or Torx). Remove the screws to pull the lens/housing away, which gives you direct access to the bulb sockets. Twist the sockets to remove and replace the bulbs.
• Side Markers & License Plate: These smaller lights typically have a simple clip-in housing or are held by one or two small screws. The lens cover can be carefully pried off or unscrewed to reveal the bulb.
• Interior Dome/Map Lights: Use a small, flat trim removal tool or a flathead screwdriver (with tape on the tip to prevent scratching) to gently pry the clear plastic lens off the overhead console. The bulbs can then be pulled straight out and replaced.

Common Lighting Issues for This Generation

The 2011-present generation of the Peterbilt 579 has a robust electrical system, but some common issues can arise.

• Connector Corrosion: The connectors for headlights and tail lights are exposed to the elements. Over time, moisture and road salt can lead to corrosion on the pins, causing intermittent or complete failure. Cleaning the connectors with an electrical contact cleaner and applying dielectric grease can prevent this.
• Rapid Turn Signal Flash (Hyperflash): If you install LED turn signal bulbs without a resistor, you will likely experience "hyperflash," where the turn signal blinks much faster than normal. This is the truck's way of telling you a bulb is out. Installing the correct load resistor will solve this.
• Voltage Irregularities: As with any heavy-duty truck, alternator or battery issues can cause voltage fluctuations that may lead to premature bulb failure. If you find yourself replacing the same bulb frequently, it’s wise to have your charging system checked.

If you encounter any issues you can't solve or prefer to have a professional handle your lighting maintenance and upgrades, use our network to find a trusted shop on Repairius.