2018 Kenworth T680 Bulb Size Guide

Quick reference

When it comes to maintaining your 2018 Kenworth T680, knowing the correct bulb sizes is crucial. This guide provides a comprehensive breakdown of the bulb types and sizes for various lighting functions on your heavy-duty truck, helping you select the right replacements whether you're upgrading to LEDs or simply replacing a burnt-out halogen.

The 2018 Kenworth T680 came with options for both halogen and LED lighting from the factory. Many trucks were equipped with full LED headlight assemblies, particularly in higher trim levels. However, some base models might still feature halogen capsules for the low and high beams. It's always best to visually inspect your current bulbs or consult your owner's manual to confirm the specific bulb type installed in your truck.

LED vs Halogen Upgrade Considerations

Upgrading from halogen to LED bulbs in your Kenworth T680 can offer significant benefits, including brighter illumination, longer lifespan, and lower power consumption. However, there are several factors to consider:

• CANBUS Errors: Modern trucks like the T680 utilize a Controller Area Network (CANBUS) system to monitor various electrical components, including lighting. When you replace a halogen bulb with an LED, the lower power draw of the LED can sometimes trigger a "bulb out" warning or flickering because the CANBUS system detects a different resistance. To remedy this, you'll often need to install CANBUS-compatible LED bulbs or use load resistors (decoders) with your new LEDs. These resistors mimic the electrical load of a halogen bulb, tricking the CANBUS system into thinking everything is normal.
• Relay and Wiring Adapters: For some aftermarket LED conversions, especially for headlights, you might need specific wiring harnesses or adapters to ensure a proper fit and connection. Always ensure any aftermarket components are designed for heavy-duty truck applications.
• Beam Pattern: Not all LED bulbs are created equal. When upgrading your headlights or fog lights, choose LEDs that are designed to replicate the beam pattern of their halogen counterparts. Poorly designed LEDs can scatter light, reducing visibility for you and dazzling oncoming drivers.

How to Replace Each Bulb

Here are some general tips for replacing common bulbs on your 2018 Kenworth T680. Always consult your owner's manual for specific instructions and safety precautions.

• Low Beam/High Beam: Access to these bulbs typically involves opening the hood and reaching behind the headlight assembly. You may need to remove a dust cap, twist to unlock the bulb, and then unplug the electrical connector. For LED assemblies, often the entire unit needs to be replaced.
• Fog Light: Access is usually from underneath the front bumper or by removing a fender liner. The bulb often twists out of its housing.
• DRL: Many T680s use integrated LED DRL strips, which are not typically user-replaceable. If equipped with separate DRL bulbs, access is similar to the turn signals.
• Front Turn Signal/Side Marker: These are usually accessible from behind the headlight assembly or by reaching into the wheel well after removing a few fasteners. Twist the socket out and pull the bulb straight out.
• Rear Turn Signal/Brake Light/Tail Light/Reverse Light: Access to these bulbs usually involves removing the lens cover from the taillight assembly. Depending on the design, you might need a screwdriver to remove screws or simply pry off the lens. Once the lens is off, twist the bulb socket out and then remove the bulb.
• License Plate Light: These are typically small, easily accessible housings often secured with a screw or clip. Remove the housing, twist out the socket, and replace the bulb.
• Dome/Map Light: These interior lights usually have a clear or frosted lens that can be carefully pried off with a small flat-head screwdriver or trim tool. Once the lens is removed, the bulb can be twisted or pulled from its socket.

Common Lighting Issues for this Generation

Owners of 2018 Kenworth T680 trucks may encounter a few common lighting-related issues:

• Flickering LEDs: If you've upgraded to aftermarket LEDs, flickering can often be attributed to CANBUS incompatibility. Installing appropriate load resistors or CANBUS-compatible bulbs usually resolves this.
• Corroded Sockets: Due to exposure to the elements, bulb sockets, particularly for exterior lights, can corrode over time, leading to intermittent connections or bulb failures. Cleaning the contacts with electrical contact cleaner or replacing the socket can fix this.
• DRL Malfunctions: While less common with OEM LED DRLs, issues can arise from wiring harnesses or the DRL control module. This often requires professional diagnosis.
• Trailer Light Issues: Given the nature of a semi-truck, problems with trailer lighting are frequent. Always check the truck's wiring harness, trailer plug, and the trailer's own wiring and bulbs if you experience issues with trailer lights.

Find a trusted shop on Repairius.