2014 Peterbilt 579 Bulb Size Guide

As a semi-truck driver, ensuring your 2014 Peterbilt 579 has fully functional lighting is a critical safety requirement, not a suggestion. Burned-out bulbs can lead to expensive tickets, downtime, and accidents. This guide provides a comprehensive list of the bulb sizes for your truck's exterior and interior, replacement tips, and common issues to watch for.

Quick Reference Bulb Size Chart

Peterbilt offered the 579 with both standard halogen reflector headlights and optional projector-style headlights, which use different bulbs. Furthermore, many 579s came equipped with factory LED lighting for marker lights and tail lights. Verify your specific configuration before purchasing replacements. The sizes below are the most common for halogen-equipped trucks.

LED vs. Halogen Upgrade Considerations

Upgrading your Peterbilt 579's lighting from halogen to LED can significantly improve visibility and reduce long-term maintenance, but it requires some care.

• CANBUS Errors: The 579's computer system (CANBUS) monitors the electrical current drawn by the lighting circuits. Since LEDs draw much less power than halogen bulbs, the system can mistakenly believe a bulb is burned out, triggering a "bulb out" warning on your dash. To prevent this, you will need to install "CANBUS-ready" LED bulbs or add an external resistor to the circuit for each bulb you replace. This is especially common for headlights and turn signals.
• Adapters and Fitment: While most LED replacement bulbs are designed to be plug-and-play, the larger heat sinks on high-power LED headlight bulbs (like H11 and 9005) may require more space behind the headlight assembly. For projector headlights, switching from HID to LED is a more complex process and may require special adapters.
• Turn Signal Hyperflash: When replacing incandescent turn signal bulbs (3157A) with LEDs, you will almost certainly encounter "hyperflash," where the signal blinks much faster than normal. This is another symptom of the low power draw. An electronic LED-compatible flasher relay or the addition of load resistors is required to restore the normal flash rate.

How to Replace Each Bulb

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

• Headlights & Front Turn Signals: Access is gained by opening the hood. The headlight assembly is held in by several bolts or clips. Once removed, the bulb sockets are twisted counter-clockwise to be removed from the housing. Wear gloves when handling new halogen bulbs to prevent skin oils from causing premature failure.
• Fog Lights: These are typically accessed from under the front bumper. You may need to remove a small splash guard to reach the back of the fog light housing.
• Tail Lights, Brake, & Reverse Lights: These are located in a combination assembly. The lens cover is usually held on by two or more screws. Once the cover is off, the bulbs can be easily accessed. For trucks with sealed LED units, the entire assembly must be replaced if a light fails.
• Side Markers: The lens cover for the side marker lights often pops off with a small flathead screwdriver, or the entire fixture can be twisted out from its mounting hole on the cab or sleeper fairings.
• License Plate Light: The small housing is typically held by two screws. Remove the housing to access the small 67 bulb inside.
• Interior Dome/Map Lights: The clear plastic lens can be gently pried off with a trim removal tool or a small flathead screwdriver to expose the festoon or bayonet-style bulb inside.

Common Lighting Issues for this Generation

The 2014 Peterbilt 579 is a workhorse, but it's not without its quirks, particularly with the lighting system.

• Connector Corrosion: Road salt, moisture, and vibration are the enemies of electrical connectors. The main headlight and tail light harness connectors are common points of failure. Symptoms include flickering lights or lights that don't work at all, even with a new bulb. Cleaning the connectors with electrical contact cleaner and applying dielectric grease can prevent this.
• Vibration Damage: Constant vibration can cause the filaments in standard incandescent bulbs to break prematurely. If you find yourself replacing the same bulb frequently, consider upgrading to a "long life" or heavy-duty version, or make the switch to a more durable LED bulb.
• Grounding Problems: A poor ground connection can cause a variety of strange lighting behaviors, such as dim lights or one light turning on when another is activated. Check the main ground straps from the cab and chassis to ensure they are clean and tight.

Don't let lighting issues compromise your safety or lead to a costly inspection failure. If you're not comfortable performing these repairs yourself, find a trusted shop near you.

Find a trusted shop on Repairius.