How to check a motorcycle ignition coil

Written by jim murkot sr.
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How to check a motorcycle ignition coil
(motor image by Klaus Eppele from Fotolia.com)

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, watertight 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.

Skill level:
Moderately Easy

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Things you need

  • Open-ended wrench set
  • Ohmmeter

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Instructions

  1. 1

    Turn off the motorcycle ignition.

  2. 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.

  3. 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.

  4. 4

    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 and warnings

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

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