A fuse box protects your Harley-Davidson motorcycle’s electrical system.
Your fuse box contains fuses that integrate into your HD’s various electrical systems, such as your headlight, to prevent meltdowns and shorts.
If your Harley’s headlight fuse detects an electrical surge in its circuit, the fuse absorbs the surplus current and blows to shed the excess power before it causes damage to your headlight circuitry.
If your Harley-Davidson motorcycle’s headlight fuse keeps blowing, it could indicate one of the problems listed below…
1. Faulty Wiring
One of the more common causes of a Harley-Davidson repeatedly blowing its headlight fuse is a short in-your-ground wire.
It’s common for the ground wire casings on older Harleys to wear with age because of changes in temperature until they crack open.
Other causes of faulty ground wires on a HD cruiser are:
- Improper storage.
- Weather-inspired corrosion.
- Lack of service inspections.
- Typical wear and tear.
Regardless, once the ground wire casing cracks open and exposes the wire, the current can escape the ground wire if it contacts the tank, motor, or metal frame.
The charge escapes the circuit through external metal objects and enters the ground – if your headlight fuse detects the short in the ground wire, it blows to protect the light’s circuitry.
Harley riders with a faulty ground wire often replace their bike’s headlight fuse multiple times only to have it blow again, as the only remedy is to repair the wire.
Here’s an example of the troubleshooting process, per a conversation between two real-life Harley-Davidson owners:
“I have a 08 [Harley-Davidson] Electra Glide. My lights are not working… checked the fuse, and the fuse was blown; I replaced the fuse and turned the bike on, and nothing fuse blew again. I have not done any troubleshooting besides reading here. It looks like a short… my question is, where should I start the troubleshooting process—
— Unplug the connector for the rear lights under the seat. The connector goes into the rear fender. Using a powered test light or multimeter, test each pin in the fender harness connector to the ground. The grounded wire/wires will be the cause of the blown fuse…it would be best if you disconnected the rear light connector under the seat to localize the problem. If the problem is still there with the rear lights disconnected, then the problem is upfront. If the problem goes away, the problem is at the rear. That narrows the search down.”
“I have a 2000 Electra Glide with EFI bought with 25k miles in November and have put almost 7k miles on it since then with Zero problems. While taking a ride this past Saturday, the bike shuts down while riding down the highway- lights, sound, power, Nothing! I drift to the shoulder, confused, hit starter nothing-check to make sure I had not hit the kill switch – fine–
–Back in ’87, I had a Sportster doing this. It turned out to be a frayed wire in the headlight that would occasionally make contact with the housing tripping the main circuit breaker. Pull over, shut her off for a few seconds, and be good to go again.”
2. Incorrectly Installed Aftermarket Upgrades
Due to the straightforward, traditional engine and transmission designs, customizing and aftermarket enhancements are common on Harley-Davidson motorcycles.
If your HD cruiser is stocked full of sound system upgrades, Power Commander enhancements, and LED lights that weren’t there when the original owner bought it brand new, chances are these parts weren’t installed by an HD dealership tech and may have been wired incorrectly.
Here’s an example of the symptoms, per a real-life Softail owner:
“I have a 2000 [Harley-Davidson] Heritage Softail, and the other day when I was riding, it just died. I towed it home and got a new battery, fuses, and terminals. I installed the new battery and the accessory fuse that was blown. I checked all the wires, but none looked cut or exposed. I tried starting my bike, and that same fuse popped, and the bike turned but didn’t start. I have no headlight (but the high beams work), no turn signal, and no horn. So, I’m wondering why my bike won’t start and why my fuse keeps blowing—
–To troubleshoot, unplug your headlight, your horn, etc. Turn your ignition switch to an accessory only. See if the fuse pops. If it does, unplug whatever added accessories you may have plugged in. Once you can get the fuse to stop popping, turn the ignition switch on. Then one at a time, plug your accessory, headlight, etc., back in. When you find what pops the fuse, unplug that item, and start plugging in the other items. If the fuse has not popped, you have potentially isolated the circuit causing the issue.”
- Sometimes, the accessory fuse isn’t rated correctly for increased electronic components.
- Other times, the aftermarket parts are hooked into the HD by splicing wires together with electrical tape or a sloppy soldering job. Your accessory circuit has a short, causing the accessory fuse to trip.
- If your shorted wires contact your Harley’s headlight circuit, your headlight fuse will also blow.
Regardless, if an aftermarket upgrade isn’t installed correctly, the resulting short can blow your Harley’s headlight fuse over and over again until it’s relaced.
3. Faulty Ignition Switch
One reason Harley-Davidsons are so popular is that they’re easy to restore, meaning their myriad HDs on the road are decades old.
Like all electrical components, ignition switches on older bikes wear down from use, as their wires started to fray from weather exposure or wear from repeated use.
One common reason a Harley-Davidson blows its headlight fuse repeatedly is due to a faulty ignition switch pulling extra battery current into its system and shedding the charge via its frayed wires. While this most commonly affects the starter fuse, the charge can jump to your other circuits, like lights, and your headlight fuse may also blow.
“Sharing in case someone else experiences this issue. For the second time in two years, my [Harley-Davidson] Road Glide loses all electrical power while riding. I slowly coasted to stop and would not respond to throttle – once stopped and turned off (kill switch), it would not allow me to restart it. The last time this happened, my mechanic found it was a blown fuse.”
Related: Harley Davidson Stalling? (7 Causes & Solutions)
4. Changing the Incorrect Fuse
While some of the older Harleys only stocked a few fuses due to a slim selection of electrical devices, modern Harleys equip whole fuse boxes full of fuses that correspond to everything from your starter, to your headlights, to your taillights, to your horn, ECU, sensor systems, stereo, navigation, heated grips, etc.
While many of the fuse boxes are clearly labeled, some riders find it difficult to figure out which fuse corresponds to which electrical system without a service manual wiring diagram of their bike.
If your Harley’s headlight fuse blows and you change it only to find your headlight’s circuitry is still lacking current, it’s possible that you replaced the wrong fuse.
5. Improper Fuse Rating
If you’ve recently replaced your Harley-Davidson’s headlight fuse, be sure you replaced it with a fuse of the same rating, or the new fuse will blow soon after you install it.
The amount of amperage a fuse allows into its circuit before it deems it a threat varies depending on the fuse’s rating.
The various fuse ratings correspond to the amount of current their associated circuits can handle.
So, for example, if your Harley cruiser’s headlight fuse is rated at 20 amps, it will blow if more than 20 amps of electricity are detected in your headlight circuit, protecting the circuit from damage.
If your HD’s headlight requires 20 amps to run and you install a 15-amp fuse into the circuit, the fuse will blow during regular operation, as it’s detecting a surge where there isn’t one.
Conversely, if you install a 30-amp fuse into a 20-amp headlight circuit, your fuse won’t blow if 25 amps surge through your Harley’s headlight circuit, risking permanent electrical damage.
6. Battery Failure
If your Harley-Davidson motorcycle’s battery is damaged, expired, or has faulty ground, it can cause multiple fuses to blow while you’re riding, impairing essential functions like headlights, starter system, brake lights, ECU, etc.
- Inspect your HD’s battery terminals for corrosion, as rust and battery acid can both interfere with their connection to your bike’s wiring harness, causing erratic current surges that can blow fuses.
- Harleys like to vibrate—a loose battery cable and a damaged or frayed battery connector can also cause your headlight fuse to blow.
- If your battery’s ground is shorted out or compromised by corrosion, its current isn’t regulated as usual; sporadic surges can blow your Harley’s headlight fuse.
If a battery failure of some sort is causing your Harley-Davidson’s headlight fuse to blow while you’re riding, the bad battery will continue to blow fuses until it’s replaced. Test a suspect battery with a multimeter to confirm if it’s the reason your HD’s headlight fuse keeps blowing.
7. Faulty Headlight Plug
One of the most common reasons a Harley-Davidson motorcycle blows a headlight fuse I due to a melted headlight plug.
The port where the headlamp plugs into the wiring harness on some Harley models is notorious for rattling loose.
Harley technicians are aware of this issue and will be able to replace the headlight plug to stop your HD’s fuses from blowing while riding.
“My amazing ’01 [Harley-Davidson] Ultra [Glide] is popping its headlight and running light fuses. I have turn signals, spot/ lights, and brake lights when I activate the break but no running lights. I’ve gone through the wiring, but every time I replace a fuse, it pops again don’t know what else it might be—
–[Sounds like a faulty] headlight plug.”
“My low beam is not working. I changed the lamp [bulb] first. But it’s still out. I have also noticed that the two driving lights on the Road King are not on—
–Driving lights are separate from the low beam. Get a wiring diagram; it may be a common ground for both… Check the headlight connector; they sometimes melt due to a loose-fitting plug.”
- Once your Harley’s headlight’s plug-in connection is compromised, traces of electricity can escape, and the plastic components in the port start to melt.
- As the internal wires become damaged, they shed electricity.
- If your headlight fuses sense large fluctuations of current in the circuitry, it will blow to prevent more damage.
- Replacing the fuse will prove to be a temporary solution, as the new fuse will blow the first time it senses current acting sporadically due to the faulty headlight plug.
Related: Harley-Davidson Won’t Idle? (10 Causes & Solutions)