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Ignition Coil
See Figure 1
  1. Detach wiring connector from cap.
  2. Turn four latches using a screwdriver and remove cap and coil assembly from lower housing.
  3. Connect an ohmmeter between distributor cap terminals "TACH" and "BAT" to test the ignition coil's primary coil. The primary coil resistance should be less than 1.0 ohm (zero or nearly zero).
  4. Make the following ohmmeter measurements using a high resistance scale:
    1. Connect an ohmmeter between the carbon button in the cap and the "GRD" terminal on the distributor cap to test the ignition coil's secondary coil. Record your reading.
    2. Connect an ohmmeter between the carbon button in the cap and the "BAT" terminal on the distributor cap to test for short in the ignition coil. Record your reading.
    3. If infinite ohms or resistance was measured in both measurements, the ignition coil is defective and needs to be replaced.
  5. If the ignition coil tests OK, it's a good idea to test the pickup coil.

Fig. 1: Checking coil resistance on the HEI system. Ohmmeter 1 shows the primary coil resistance connection. Ohmmeter 2 shows the secondary resistance connection. 1980 models shown, others similar

These resistance checks will not disclose shorted coil windings. This condition can be detected only with scope analysis or a suitably designed coil tester. If these instruments are unavailable, replace the coil with a known good coil as a final coil test.
 
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