Gasoline-powered vehicles manufactured by General Motors up until the late 1990s rely upon an ignition coil. Consisting of primary and secondary coils, this component induces the high voltage necessary for spark plugs to ignite the fuel and air mixture for each cylinder in the engine. These 12 volt coils have been and still are made by AC Delco, a subsidiary of General Motors. When an ignition system is not functioning properly or when replacing said component, it is advised that you test the primary and secondary coils.
Set up the digital multimeter. Using the instructions supplied with the meter, set it up as an ohmmeter and connect the probe test leads. Also, make sure you know how to switch between the appropriate ranges needed for this test. Usually, the 200 ohm and the 20,000 ohm ranges will suffice for the primary and secondary coils, respectively.
Set the multimeter to the 200 ohm range. On the coil package, there are positive and negative terminals for the primary coil. Touch the respective positive and negative leads from the digital multimeter to them. A valid reading from the meter is typically within the range of 0.75 and 0.81 ohms. If you have a copy of the specifications for your particular model of Delco coil, use that information to know what is an acceptable reading for both the primary and secondary coils.
Remove the test leads from the coil and set the multimeter to the 20,000 ohm range to test the secondary coil resistance. Touch one test lead to either outer terminal and touch the remaining test lead to the connector on the high tension tower, which is in the centre of the component. Depending upon the model of Delco coil, an acceptable output reading from the meter is typically within the range of 9,000 and 11,000 ohms.
Evaluate the results of the tests. If the Delco coil passes both of these tests, then it is suitable for use. Otherwise, it should be replaced.
Only test an ignition coil that has been disconnected from the rest of the ignition system.