Ignition Coils
About Ignition Coils
The ignition coil turns the battery's low voltage into the high-voltage pulse that jumps the gap at the spark plug. When one weakens, the bike can misfire under load, start hard, idle roughly or cut out when hot. Riders replace coils for those faults, and some Harley owners fit a higher-output coil when they change the ignition or the engine.
Coils come in a few layouts. An external coil sits on the frame and sends its spark through a plug wire to a cap on the spark plug. A coil-on-plug unit mounts directly on the plug with no wire between them. On Harley-Davidsons you will see single-fire and dual-fire listings. These describe how the ignition system triggers the spark, and the coil has to match the ignition it plugs into. Some listings also show an ohm rating for the coil's primary winding, which should agree with what the ignition or coil maker calls for. Replace a tired plug wire or cap while you are there.
Brands in this category include Colony, Andrews, HardDrive, Drag Specialties and ACCEL. Related parts are Spark Plugs, Ignition Wires, Caps & Boots and Ignition Kits. Coils are specific to the engine, so pick your machine in the Ride Finder at the top of the page, and see our guide on why a part did not fit before ordering.
FAQs on motorcycle ignition coils
How can I tell if an ignition coil is bad?
Common signs are misfires, hard starting, a weak or missing spark and stalling that gets worse when the engine is hot. Worn spark plugs, cracked plug wires and loose caps cause the same symptoms, so check those first. A multimeter reading against the service manual's resistance figures can confirm a bad coil.
What does single-fire versus dual-fire mean on a Harley coil?
It refers to how the ignition system fires the spark plugs. A single-fire setup times each plug separately, while a dual-fire setup fires both plugs together. A coil has to be made for the type your ignition uses, so check the listing and your model's ignition before choosing.
What is a coil-on-plug ignition coil?
A coil-on-plug coil mounts straight onto the spark plug, so there is no plug wire between them. Many modern engines use them, with one coil for each cylinder. They are model-specific, so match the part to your exact bike and engine.
Will a high-output coil improve my motorcycle's performance?
Not on its own. A stock engine in good condition already gets an adequate spark. A higher-output coil mainly helps when the engine has been modified or the original ignition is weak. It must also suit your ignition module, so follow the maker's fitment notes.
Should I replace both coils on a twin at once?
It is not required, but both coils have the same age and wear. If one has failed, many owners replace the pair, along with the plugs and plug wires, to avoid another failure soon after. Check the service manual for your model.
