Test the ignition coil

An ignition coil contains two sets of copper winding: the primary and the secondary. When current is sent to the ignition coil from the ignition module or E.C.M., the primary winding energizes and creates a strong magnetic field. The secondary winding increases the voltage as the magnetic field is created and sends a high energy spark to the spark plug. Problems with primary or secondary winding will not allow a conductive path for current and the spark plugs will not work.

To test and inspect the ignition coil:

1. Visually inspect the ignition coil for cracks, hot spots (melted areas), and carbon buildup. Replace if necessary.
2. Measure the resistance of the primary winding. Set your meter to read ohms and place your red probe on the positive post of the coil. Place the black probe on the negative post. Your reading should be between three and four ohms.
3. Measure the resistance of the secondary winding. Place your red probe on the positive post of the coil. Place the black probe on the spark plug wire terminal. Your reading should be between 10,000 and 20,000 ohms

Later model Sportsters use a wiring connector instead of individual posts on the coil. To measure this styles resistance, you'll need to unplug the connector and measure the resistance at the four prongs on the coil. You'll need a copy of your year's service manual or wiring diagrams from your local Harley dealership for prong locations.