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How to Check a Motorcycle Ignition Coil

by Jim Murkot Sr.

The ignition coil on a motorcycle serves to step up the relatively low battery voltage to the high voltage needed to fire a spark plug. Coils are generally a sealed, water-tight component. As such, they are generally not a repairable item. Routine checks on a coil are not necessary. They should be tested as part of a troubleshooting procedure whenever the motorcycle becomes difficult to start or runs rough. Testing them tends to be relatively simple and involves the use of an ohmmeter.

Step 1

Turn off the motorcycle ignition.

Step 2

Disconnect the spark plug wires from the coil by hand. Disconnect the two smaller primary wires from the coil using an open-ended wrench.

Step 3

Measure the resistance between the coil connections for the spark plugs with an ohmmeter. The resistance should be 0.5 to 3 ohms. A resistance outside of this range indicates a broken coil.

Measure the resistance between the two smaller primary wire connections on the coil with an ohmmeter. The resistance should be 6,000 to 12,500 ohms. Again, a resistance outside of this range indicates a broken coil.

Tips

  • Try testing the coil after the motorcycle has been run and the coil is hot. The resistances measured across the terminals could change under heat.
  • Find exact ranges for the resistance on a coil in the service manual for your particular make and model of motorcycle.

Warning

  • Use caution when working around electricity. Remove all watches and rings to help guard against shock.

Items you will need

  • Open-ended wrench set
  • Ohmmeter

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