Distributor Cap & Coil Testing

Remove distributor cap and coil assembly by removing wiring harness connector, battery lead, and cap-to-housing latches. Inspect rotor, cap and coil assembly for arc-over. Replace parts as necessary.
To test coil primary resistance, connect one ohmmeter lead to battery terminal on distributor cap. See Fig 1. Connect other lead to tach terminal of distributor cap. Ohmmeter reading should be 0.4-1.0 ohm. Connect ohmmeter leads to tach terminal and ground. Reading should be infinity. If either reading is not to specifications, replace ignition coil.
To test coil secondary resistance, connect one ohmmeter lead to coil secondary contact (cap button). See Fig 1. Connect other lead to tach terminal. Ohmmeter reading should be infinity.

Fig 1: Distributor Cap and Coil Testing Connections for Delco-Remy HEI Distributor
Courtesy of GENERAL MOTORS COMPANY
Move ohmmeter lead from tach terminal and attach it to ground terminal. Secondary-to-ground ohmmeter reading should be 6, 000-30, 000 ohms. If these tests are not to specifications, replace ignition coil.
NOTE: Replace ignition coil only if readings in both steps 3) and 4) are infinity.