A dark section of roofline in the middle of December almost always has one of a handful of causes, and most of them can be identified without climbing anything.
This guide walks through the common failures in roughly the order to check them, what you can safely look at from the ground, and where the line is between “check it yourself” and “call someone.”
Most of these causes leave a clue in how the failure shows up: whether the whole display is dark or just part of it, whether it happened after rain or wind, and whether it is a one-time event or something that keeps coming back in the same spot.
Reading those clues first, before touching anything, usually narrows the list down to one or two likely causes before you even get outside.
Start with the outlet: GFCI trips
If the whole display is dark, the outlet is the first thing to check, not the lights themselves. Outdoor outlets are required to have GFCI (ground-fault circuit interrupter) protection, and that protection trips the circuit the moment it senses current going somewhere it should not, usually through moisture.
Reset it once, at the outlet or at the breaker panel if the GFCI is there instead. If the lights come back on and stay on, that was the whole problem. If the outlet trips again immediately, stop resetting it.
A GFCI that will not hold a reset is telling you there is an active fault, most often water sitting in a plug connection or a damaged cord, and repeatedly forcing the reset does not fix that fault, it just delays finding it.
Wet connections
Water is the single biggest cause of intermittent Christmas light failures. A plug-to-plug connection sitting at the bottom of a slope where snowmelt runs past it, a clip joint on a north-facing eave that never fully dries out, or a connector left resting directly on the ground all create the same problem: moisture bridges the connection and either shorts it out or trips the GFCI protecting it.
From the ground, you can often spot this: a connection point sitting in a puddle, packed against wet mulch, or lower than the roofline it is meant to be clipped to.
Lifting a low connection off wet ground and onto a hook or a dry surface is a reasonable fix. A connection you cannot reach without a ladder is not something to force from underneath; note where it is and have it addressed properly.
A single failed bulb or section
Older incandescent strands are wired in series, meaning one dead bulb can take out everything downstream of it on that string. Most modern LED sets are wired with each bulb on its own shunt or with sections protected by an in-line fuse in the plug, so a single failure usually kills a shorter run, not the whole strand.
Either way, the symptom looks the same from a distance: a clean gap where lights should be. We cover the mechanics of this in detail, including how to check the fuse in the plug, in why half a strand goes dark.
Timers and controllers
If the display comes on at the wrong time, does not turn off, or does not come on at all while the outlet itself is live, the timer or controller is the likely culprit, not the lights.
Mechanical timers drift or stick over a season of cold nights; digital ones lose their programming if power is interrupted, or the battery backup that holds the clock fails. Checking the timer’s current time and program from the ground, and confirming it is actually receiving power, rules this cause in or out in a couple of minutes.
Overloaded circuits
Plugging several strands into the same outlet, especially on an older home with fewer outdoor circuits, can pull more current than that circuit is rated for. The breaker trips, or, short of tripping, the strands at the far end of a long daisy chain run dim because voltage has dropped across all the connections in between.
If lights are noticeably dimmer the farther they are from the plug, or a breaker (not a GFCI) is tripping, the circuit is carrying more than it should. Splitting the load across two outlets or circuits, rather than adding an extension cord and more strands to the same one, is the fix.
Extension cords and outdoor ratings
An overloaded circuit and a failing extension cord often look identical from the ground: dim lights, a section that flickers, or an outlet that will not stay on. Not every extension cord is rated for outdoor use or for the load a full display draws, and a light-duty indoor cord pressed into outdoor service over a few cold weeks is a common, easy-to-miss cause of both problems.
Checking that any cord in the run is rated for outdoor use and for the wattage of what is plugged into it is worth doing before assuming the fault is in the lights themselves. A cord that feels warm to the touch while lights are running is a sign it is carrying more than it should, not a sign to ignore.
Wind and clip failures
Clips are matched to a specific roof or gutter edge for a reason: a clip designed for a shingle edge does not hold the same way on a metal fascia or a tile lip, and a clip reused for one season too many loses its grip. Wind finds whatever connection is weakest first.
A section sagging, swinging loose, or missing entirely after a windy night is a clip failure, not an electrical one, and the fix is a matter of re-securing with the right clip for that edge rather than diagnosing wiring.
What you can safely check from the ground
Before assuming the worst, a short ground-level check covers most of the causes above:
- Confirm the outlet is on and reset any tripped GFCI once.
- Check that every plug connection you can see from the ground is actually seated, not just resting together.
- Look for connections sitting in standing water or wet ground.
- Check the timer’s clock and program.
- Look for an obviously sagging or missing section, which points to a clip failure rather than a bulb failure.
- Note whether the dim or dark section is close to the plug end or far from it, which helps tell a fuse or connector problem from a voltage-drop problem.
None of this requires a ladder or getting on a roof. Every item on that list can be done standing on the ground, looking up at the display rather than climbing toward it.
If the check points to something at height or something you cannot reach safely, that is the point to stop and call rather than improvise a fix from a ladder in December.
When to call someone
A few situations are worth calling a professional rather than continuing to troubleshoot:
- A GFCI that trips again immediately after a reset, which usually means an active short or a damaged connection.
- Any exposed or damaged wiring, rather than just a loose connection.
- A section that failed at height, on a roofline or second-story fascia, where a proper fix means being up there safely with the right tools.
- A recurring problem in the same spot every year, which usually means the underlying cause was never actually fixed, only patched.
If Glow Forward installed your lights, in-season repairs are already part of the package under the 5-Star Guarantee: call, we come out, we fix it.
If you installed your own lights or had someone else install them, our repair and maintenance service covers diagnosing and fixing exactly the causes above, without you needing to get on a ladder to find out which one you have.
After the season: takedown matters too
A lot of next year’s failures start with how a display comes down and gets stored this year. Loose bulbs, tangled runs, and strands stored somewhere that gets too hot or too damp all show up as mysterious faults next November.
See storing Christmas lights after takedown for how to take a display down in a way that makes it easier to troubleshoot, and less likely to need it, next season.
If you would rather not deal with any of the above, from the initial install through the January takedown, see our Christmas light installation service.
Written by Michael Preston, Glow Forward Holiday Lighting. More from the blog