Under cabinet lights are a fantastic addition to any kitchen or workspace, offering practical illumination and often enhancing the overall aesthetic. However, like any electrical fixture, they can encounter issues. The good news is that many common problems with under cabinet lighting are relatively straightforward to diagnose and fix yourself, saving you the hassle and expense of calling an electrician. Most often, issues stem from loose connections, faulty bulbs, or a power supply problem. We’ll walk you through how to troubleshoot these common hiccups without needing a specialized degree.

Understanding Your Under Cabinet Lighting System

Before diving into repairs, it helps to understand the basic components of your under cabinet lighting. This isn’t just about knowing what’s what; it helps you pinpoint where a problem might originate.

Types of Under Cabinet Lights

There are a few main types of under cabinet lights, and each has slightly different repair considerations.

• Puck Lights: These are small, circular lights, often LED, that can be recessed or surface-mounted. They often operate on low voltage and might be powered by a central transformer.
• Strip Lights (LED Strips): Flexible strips with numerous small LED chips. They are typically adhesive-backed and can be cut to length. They almost always require a 12V or 24V power supply (driver).
• Bar Lights (Rigid LED Bars): Similar to strip lights but housed in a rigid, often aluminum, casing. They can be plug-in or hardwired.
• Fluorescent Tube Lights: Older installations might still use slim fluorescent tubes. These require a ballast to regulate current and ignite the bulb.
• Halogen/Xenon Lights: Less common now due to energy consumption, but older systems might have these. They generate more heat and often require a transformer for low-voltage versions.

Understanding which type you have will inform your troubleshooting steps, especially concerning power supplies and bulb replacements.

Essential Components of Under Cabinet Lighting

Regardless of the type, most under cabinet lighting systems share core components.

• Light Fixture/Bulb: This is the part that actually emits light. It could be an LED chip, a fluorescent tube, a halogen bulb, or a Xenon bulb.
• Power Supply/Driver/Transformer/Ballast: This component converts your household AC voltage (typically 120V in North America) into the voltage required by your lights. LEDs usually use a “driver” or “power supply” (often 12V or 24V DC), while halogen/Xenon might use a “transformer” (low voltage AC), and fluorescents use a “ballast.” If your lights are plug-in, this component might be integrated into the plug-in adapter. If hardwired, it’s often a separate box.
• Wiring: Connects the power supply to the individual light fixtures. This can be low-voltage wiring for LEDs or higher-voltage wiring for some fluorescent or direct-wire systems.
• Switch: Controls the flow of power to the lights. This could be a wall switch, an inline switch, a touch sensor, or even a motion sensor.
• Connectors: Used to join wires, connect lights in series or parallel, or attach wires to the power supply.

Knowing these parts helps you systematically check each one when something goes wrong.

Common Problems and Initial Checks

When your under cabinet lights aren’t working as expected, don’t panic. Many issues have straightforward explanations. Always remember to turn off the power at the breaker before performing any inspections or repairs involving wiring.

Lights Not Turning On At All

This is arguably the most common and frustrating problem. If your lights are completely dark, start with the basics.

• Check the Power Switch: It sounds obvious, but ensure the switch is actually in the “on” position. Sometimes it’s accidentally flipped, or if it’s a dimming switch, it might be turned all the way down.
• Verify Power at the Outlet/Circuit Breaker: If your lights are plug-in, ensure the outlet is live by plugging in another working appliance. If hardwired, check your home’s electrical panel. Has a circuit breaker tripped? If so, reset it. If it trips again immediately, there’s a short circuit somewhere, and you should call an electrician.
• Inspect the Power Supply/Driver: For low-voltage LED or halogen systems, the power supply or driver is a common failure point. Some drivers have an indicator light; if it’s off, the driver might not be receiving power or has failed. If it’s warm to the touch (and shouldn’t be), it might be overloaded or failing.
• Loose Connections: This is a big one. Over time, vibrations or even initial imperfect installations can loosen wire nuts, terminal connections, or plugs. Gently wiggle connections at the power supply, between light segments, and at the switch.
• Faulty Bulb/Fixture: If you have multiple fixtures on one circuit and only one isn’t working, that specific bulb or fixture is likely the culprit. For fluorescent tubes, look for darkened ends or a flicker before failure. For LEDs, sometimes individual chips fail, but if the whole unit is dark, it’s usually a power issue or the entire fixture has failed.

Flickering or Dim Lights

Flickering or dimming can be even more annoying than total darkness because it suggests an intermittent problem.

• Loose Connections (Again): Just like with no power, loose wiring is a prime suspect for flickering. A connection that’s almost making contact can cause intermittent power. Focus on the connections closest to the flickering light.
• Aging Bulb/Fixture: Fluorescent tubes are notorious for flickering towards the end of their life. Halogen and Xenon bulbs can also flicker as their filaments degrade. While LEDs have a long lifespan, cheap LED drivers or fixtures can sometimes cause flickering, especially if they are overloaded or nearing the end of their design life.
• Incompatible Dimmer Switch: If your lights are dimmable, ensure your dimmer switch is compatible with your specific type of lights (e.g., “ELV” or “MLV” for low voltage, “LED compatible” for LEDs). Using a standard incandescent dimmer with LEDs can cause flickering, humming, or even damage the LEDs.
• Failing Power Supply/Driver/Ballast: A power supply that’s starting to fail might not provide consistent voltage, leading to flickering or dimming. For fluorescent lights, a failing ballast is a very common cause of flickering.
• Voltage Drop: If you have a very long run of low-voltage LED strip lights, especially with thin wiring, you might experience voltage drop, where the lights further down the line are dimmer. This usually requires a more robust power supply or adding power injection points.

Lights Humming or Buzzing

That annoying hum can quickly make you regret installing under cabinet lights.

• Incompatible Dimmer Switch: This is the most frequent cause of humming, especially with LED or low-voltage systems. Many standard dimmers aren’t designed to handle the low loads or the electronic components of LED drivers, leading to an audible hum. Upgrading to an LED-compatible dimmer (often called ELV or MLV for low-voltage systems) is usually the solution.
• Failing Ballast (Fluorescent Lights): Older fluorescent ballasts are notorious for humming. If you have fluorescent lights and they’re humming loudly, the ballast is likely on its way out and needs replacement.
• Failing Power Supply/Driver: While less common than a ballast, an electronic LED driver that’s failing can sometimes produce a hum or buzz.
• Loose Transformer/Fixture: Sometimes the hum isn’t electrical but mechanical. A transformer or fixture that isn’t securely mounted can vibrate against the cabinet, amplifying any internal electronic noise. Ensure all mounting screws are tight.

Easy Repair Tips for Common Issues

Now that we’ve identified the problems, let’s get into the practical steps to fix them. Remember the golden rule: Always turn off the power at the circuit breaker before beginning any electrical work.

Bulb and Fixture Replacement

This is often the easiest fix and a good starting point if you suspect a single light is out.

• Fluorescent Tubes:
• Removal: Gently twist the tube 90 degrees to disengage it from the sockets, then pull it out.
• Installation: Align the pins on the new tube with the slots in the sockets, push firmly, and twist 90 degrees until it locks into place.
• Troubleshooting: If a new tube doesn’t work, the problem is likely the ballast. Replacing a ballast can be a bit more involved, often requiring disconnecting and reconnecting several wires. Make sure the replacement ballast matches the specifications of the old one (e.g., number of lamps, wattage).
• Halogen/Xenon Bulbs:
• Removal: These often have two small pins (bi-pin) or screw into a socket. For bi-pin bulbs, grasp the bulb with a cloth (to avoid touching the glass directly, as oils can cause hot spots and premature failure) and pull straight out. For screw-in types, just unscrew.
• Installation: Insert the new bi-pin bulb carefully, ensuring the pins align with the holes. Screw in screw-in types.
• Troubleshooting: If the new bulb doesn’t light, check the transformer if it’s a low-voltage system.
• LED Puck/Bar/Strip Lights:
• Puck/Bar Lights: If these are individual units, often the entire unit is replaced. Some are plug-and-play, others are hardwired. If hardwired, ensure power is off, disconnect the old fixture, and connect the new one, matching wire colors (black to black, white to white, green/bare to ground).
• LED Strips: If a section of an LED strip has failed, and the rest is working, it’s often easiest to replace that segment or the entire strip. LED strips are usually designed to be cut at specific marked points. You might need new connectors to reattach sections or to attach a new strip to your power supply.

Checking and Tightening Connections

Loose connections are a major cause of intermittent issues or total failure.

• At the Power Supply/Driver/Ballast:
• Turn off power at the breaker.
• Locate your power supply unit. It might be hidden inside a cabinet, above the cabinet, or accessible in a junction box.
• Carefully check all wire connections going into and out of the power supply. These are often secured with screw terminals or push-in connectors.
• Gently tug on each wire to ensure it’s securely seated. If using screw terminals, tighten them. If push-in, ensure the wire is fully inserted.
• Between Light Fixtures (for daisy-chained systems):
• Many under cabinet light systems are “daisy-chained,” meaning power flows from one fixture to the next.
• Check the connections where each fixture connects to the next. These can be small plug-in connectors, wire nuts, or terminal blocks.
• Ensure all plugs are fully seated and wire nuts are tight. If you find a loose wire nut, remove it, twist the wires together more firmly, and replace the wire nut.
• At the Switch:
• Turn off power at the breaker.
• Remove the switch plate cover.
• Carefully pull the switch out of the wall box.
• Check all wire connections on the back or sides of the switch. Ensure they are tight. If wires are wrapped around screws, ensure they are clockwise and secure.

Diagnosing and Replacing Power Supplies/Drivers/Ballasts

If bulbs are good and connections are tight, the power supply is the next likely suspect.

• Identifying Failure:
• No output voltage: If you have a multimeter, you can test the output voltage of the power supply. With the unit powered ON (be extremely careful as AC voltage is present), test the DC output side (for LED drivers) or AC output (for transformers). If there’s no voltage or significantly reduced voltage compared to the rating, the unit has failed.
• Physical signs: Look for burnt smells, swollen casings, or scorch marks on the unit.
• Flickering/Humming (as discussed above): These can be signs of impending failure.
• Replacement Process:
• ALWAYS turn off the power at the circuit breaker.
• Disconnect wiring: Carefully note or photograph how the old unit is wired. There will be an input side (usually 120V AC household current) and an output side (low voltage DC for LEDs, low voltage AC for halogens, or specific outputs for fluorescents).
• Remove old unit: Unscrew or unmount the old power supply.
• Install new unit: Mount the new power supply in the same location.
• Connect wiring: Connect the input wires (black to black, white to white, ground to ground) and the output wires (observing polarity for LEDs: positive to positive, negative to negative).
• Crucial Tip: When replacing an LED driver, ensure the new driver’s wattage capacity is equal to or greater than the total wattage of your LED lights. Also, match the output voltage (e.g., 12V or 24V). For fluorescent ballasts, ensure the new ballast matches the old one’s lamp type, number of lamps, and wattage.

Addressing Dimmer Switch Issues

Dimmers are great but can be a source of problems if not matched correctly.

• Incompatibility: If you’re experiencing flickering, buzzing, or inconsistent dimming, especially after upgrading to LED lights, the dimmer is the prime suspect.
• Upgrade to an LED-Compatible Dimmer:
• Turn off power at the breaker.
• Remove the old dimmer: Disconnect the wires, noting how they were connected (line, load, ground, and sometimes a traveler for 3-way switches).
• Install the new dimmer: Follow the wiring diagram provided with your new LED-compatible dimmer switch. These dimmers are designed to handle the low wattage and electronic characteristics of LEDs. They often specify being “ELV” (Electronic Low Voltage) or “MLV” (Magnetic Low Voltage) for low-voltage systems, or simply “LED Compatible.”
• Test: Restore power and test the new dimmer. If problems persist, you might have an issue with the LED driver itself or the lights are not truly dimmable.

Safety First: Essential Precautions

Working with electricity always carries risks. Taking proper precautions is not just recommended, it’s essential for your safety.

Always Turn Off Power at the Breaker

This cannot be stressed enough. Before you touch any wiring, fixture, or power supply, go to your main electrical panel and switch off the circuit breaker that controls your under cabinet lights. If you’re unsure which breaker it is, turn off the main breaker to the entire house, or use a non-contact voltage tester to confirm no power is present at the fixture.

Use Insulated Tools

Ensure any screwdrivers, pliers, or wire strippers you use have insulated handles. This provides an extra layer of protection against accidental shocks, even if the power is supposedly off.

Test for Power Before You Touch

Even after flipping the breaker, it’s good practice to use a non-contact voltage tester to confirm that no electricity is flowing to the wires you’ll be working on. This provides peace of mind and guards against faulty breakers or misidentified circuits.

Don’t Overload Circuits

When replacing power supplies or adding more lights, be mindful of your circuit’s capacity. Each circuit breaker is rated for a certain amperage (e.g., 15A or 20A). Ensure the total wattage of your lights (and any other appliances on that circuit) doesn’t exceed 80% of the circuit’s capacity to avoid tripping breakers or creating a fire hazard.

Consult an Electrician When in Doubt

If you’re uncomfortable at any point, encounter persistent problems, or suspect an issue with your home’s main wiring, don’t hesitate to call a licensed electrician. Some problems, like persistent tripping breakers or exposed damaged wiring, are beyond DIY repair and require professional attention for safety. It’s always better to be safe than sorry.