Do I Need a Load Resistor With My JW Speaker LED Tail Lights on a Kenworth?
Most Installations Do Not Need an External Resistor But Here Is How to Confirm
Maybe — but probably not right away. Whether you need one depends on what your truck is doing after the install. Here is how to figure it out.
Most Installs Don't Need One
JW Speaker LED tail lights for commercial trucks are built with the right resistance calibration for standard Kenworth wiring. In a typical installation — one light per circuit, nothing else modified — you usually won't need to add anything extra.
You Might Need One If...
Your dash is showing a "tail light out" warning even though the light works. This is the most common sign. Your truck's electrical system monitors current draw to detect burned-out bulbs. LED lights pull less current than halogen, so the system can misread a perfectly working LED as a failed bulb. A load resistor corrects this by bringing the current draw back up to what the truck expects.
You've upgraded multiple lights at once. If you've replaced your headlights, marker lights, and tail lights all with LEDs, the combined low current draw across all those circuits can add up — even if each individual light passes the check on its own. When everything is LED, you may need a resistor even if you didn't need one with just one upgrade.
Your Kenworth has a more sensitive monitoring system. Some models are pickier than others. If you're seeing warnings that don't make sense and your wiring checks out, the monitoring system sensitivity may be the culprit.
Quick Way to Diagnose the Problem
Swap the factory halogen tail lights back in temporarily. If the dashboard warning goes away with the halogen lights installed, the LEDs are the cause. If the warning stays even with the factory lights, the problem is somewhere else in the truck — not the lights.
One Thing You Should Never Do
If your JW Speaker tail light has a built-in resistor, do not open the housing to replace or swap it. Opening the housing voids the warranty and permanently breaks the factory weatherproof seal. Leave it sealed — always.
Not Sure What Resistor You Need?
Don't guess on resistor sizing — using the wrong one can make the problem worse or cause heat issues. Contact your authorized JW Speaker distributor or a qualified truck electrician and give them your truck's make, model, year, and the JW Speaker part numbers you have installed. They can tell you exactly what you need.
Find a distributor: https://www.jwspeaker.com/dealers/distributors/