2020 Peterbilt 389 Bulb Size Guide

Quick reference

Maintaining proper lighting is crucial for the safety and legality of your 2020 Peterbilt 389. This guide provides a comprehensive breakdown of bulb sizes for various lighting functions, helping you with replacements and potential upgrades. The Peterbilt 389, known for its classic styling and robust performance, offers both halogen and optional LED lighting from the factory. Understanding these differences is key when selecting replacement bulbs.

Halogen vs. LED OEM Differences

The 2020 Peterbilt 389 typically comes standard with traditional halogen bulbs for most exterior and interior lighting. However, Peterbilt offers optional LED lighting packages, particularly for headlights, fog lights, and some marker lights. If your truck came with the optional LED package, replacing a bulb would often mean replacing an entire LED assembly rather than a single bulb. For standard halogen setups, individual bulb replacement is straightforward.

For headlights, standard models will utilize H11 for low beams and H1 for high beams. If your 389 has the factory LED headlight option, these will be sealed LED units and not individual bulbs. Similarly, fog lights, DRLs, and even some turn signals might be LED assemblies if the truck was specified with those options. Always visually inspect your current bulbs or assemblies to confirm the type before purchasing replacements.

LED vs Halogen Upgrade Considerations

Upgrading from halogen to LED bulbs in your 2020 Peterbilt 389 can offer numerous benefits, including brighter light, longer lifespan, and improved energy efficiency. However, there are important considerations to keep in mind:

• CANBUS Errors: Modern vehicles, including the Peterbilt 389, use a Controller Area Network Bus (CANBUS) system to monitor various electrical components, including lights. Halogen bulbs draw more power than LEDs. When you install LED bulbs, the reduced power draw can trigger a "bulb out" warning or hyper-flashing (for turn signals) because the CANBUS system interprets the lower current draw as a burnt-out bulb. To avoid these issues, you'll typically need to install CANBUS-compatible LED bulbs or load resistors/decoders with your new LED bulbs. These devices mimic the electrical load of a halogen bulb, preventing error messages.

• Adapters Needed: Some aftermarket LED bulbs may require specific adapters or wiring harnesses to fit correctly into the housing or connect to the factory wiring. Always check the product description for compatibility with the 2020 Peterbilt 389.

• Beam Pattern: While LEDs are brighter, their light output can differ from halogens. Ensure any aftermarket LED headlights or fog lights produce a proper beam pattern to avoid blinding oncoming traffic and to provide effective illumination of the road.

How to Replace Each Bulb

Replacing bulbs on your Peterbilt 389 generally involves a few common steps. Always ensure the vehicle is turned off, and for exterior lights, it's often easier to access them by opening the hood or, in some cases, by removing a portion of the inner fender lining.

• Low Beam/High Beam Headlight: Access from behind the headlight assembly, usually by removing a dust cap or cover. Disconnect the electrical connector, unclip the bulb (often a spring clip), remove the old bulb, and insert the new one without touching the glass (for halogens). Reassemble in reverse order.

• Fog Light: Typically accessed from behind the bumper or through the wheel well. You may need to remove a few screws or clips to gain access. Disconnect the harness and twist or unclip the bulb.

• DRL (Daytime Running Light): Often integrated into the headlight assembly or a separate housing. Access can vary but usually involves twisting and pulling the bulb holder.

• Front Turn Signal: Commonly found within the headlight housing or a separate amber lens assembly. Twist the bulb holder counter-clockwise to remove.

• Rear Turn Signal/Brake Light/Tail Light/Reverse Light: These are usually in a combined taillight assembly. Remove the screws securing the taillight housing, carefully pull it away from the body, twist the bulb holders, and replace the bulbs. For combination bulbs like the 3157, ensure the correct orientation.

• License Plate Light: Typically involves removing a clear lens cover (often held by screws) to access the bulb.

• Side Marker Light: Often twist-lock assemblies. Twist the lens or the bulb holder to remove and replace.

• Dome/Map Light: These interior lights often have a clear plastic lens that can be carefully pried off with a plastic trim tool or small flathead screwdriver to access the bulb.

Common Lighting Issues for This Generation

Owners of the 2020 Peterbilt 389 might encounter some common lighting-related issues, particularly as the trucks age or if modifications are made:

• Intermittent Light Failure: Often due to loose connections, corroded sockets, or failing bulbs. Check the wiring harness and clean any corrosion.

• Shorter Bulb Lifespan: While Peterbilts are durable, continuous vibration from long-haul driving can reduce the lifespan of halogen bulbs. Upgrading to quality LEDs can mitigate this.

• "Bulb Out" Warnings After LED Upgrade: As mentioned earlier, this is a common CANBUS issue when installing non-CANBUS-compatible LEDs without load resistors.

• Dimming or Flickering Lights: Could indicate a failing alternator, battery issues, or a poor ground connection. Ensure your electrical system is in good health.

• Condensation in Light Housings: Over time, seals around light housings can degrade, allowing moisture to enter and cause condensation, which can reduce light output and potentially damage bulbs or LED components. Inspect seals and replace if necessary.

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