PRIMARY CIRCUIT WITH VOLTMETER
A quick, tentative check of the 12 volt ignition primary circuit (including ballast resistor) can be made with a simple voltmeter, as follows:
- With engine at normal operating temperature, but stopped, and the distributor side of the ignition coil grounded using a jumper wire, hook up a voltmeter between the ignition coil (switch side) and a good ground.
- Jiggle the ignition switch (switch ON) and watch the meter. An unstable needle will indicate a defective ignition switch.
- With the ignition switch ON (but engine still stopped) the voltmeter should read 5.5 to 7 volts for 12 volt systems.
- Crank the engine. Voltmeter should read at least 9 volts during cranking period.
- Now remove the jumper wire from the coil. Start the engine. voltmeter should read from 9.0 volts to 11.5 volts (depending upon generator output) while running.
To check ignition coil resistance, primary side, switch ohmmeter to low scale. Connect the ohmmeter leads across the primary terminals of the coil and read the low ohms scale.
Coils requiring ballast resistors should read about 1.0 ohm resistance. 12 volt coils, not requiring external ballast resistors, should read about 4.0 ohms resistance.SECONDARY CIRCUIT WITH OHMMETER
To check ignition coil resistance, secondary side, switch ohmmeter to high scale. Connect one test lead to the distributor cap end of the coil secondary cable. Connect the other test lead to the distributor terminal of the coil. A coil in satisfactory condition should show between 4K and 8K on the scale. Some special coils (Mallory, etc.) may show a resistance as high as 13K. If the reading is much lower than 4K, the coil probably has shorted secondary turns. If the reading is extremely high (40K or more) the secondary winding is either open, there is a bad connection at the coil terminal, or resistance is high in the cable.
If both primary and secondary windings of the coil test good, but the ignition system is still unsatisfactory, check the system further.
REMOVAL & INSTALLATION
- Disconnect the negative battery cable.
- Remove the ignition switch-to-coil lead from the coil.
- Unfasten the distributor leads from the coil.
- Remove the screws which secure the coil to the engine, then lift the coil from the vehicle.
- Position the coil assembly to the engine and secure using the retaining screws.
- Connect the distributor leads to the coil.
- Connect the ignition switch-to-coil lead.
- Connect the negative battery cable.