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Battery CD Ignitions without Points Three Cylinder Engines with 332-4796/393-4797 Battery Type Ignitions

Note: A CD Tester by CDI Electronics (511-9701) or Merc-o-Tronics can be used to test the CD module, distributor cap, rotor button and spark plug wires on the engine while the Trigger Tester by CDI can be used to test the distributor trigger.

SERVICE NOTE: Check the battery voltage at approximately 3500 RPM, MAXIMUM reading allowable is 16 volts and minimum is 12V. Running below 12V or over 16 volts will damage the ignition. Check for loose connections or a bad battery. Maintenance free batteries are NOT recommended for this application.

Engine Wiring Connection for Testing Ignition Module


  • 1.

    Clean all battery connections and engine grounds.

  • 2.

    Disconnect the mercury tilt switch and retest. If the ignition works properly, replace the mercury switch.

  • 3.

    Connect a spark gap tester to the spark plug wires and check for fire on all cylinders. If some cylinders fire and not others, the problem is likely in the distributor cap, rotor button or spark plug wires.

  • 4.

    Perform a voltage drop test after the engine is repaired to see if there is a problem with the voltage going to the CD module. At cranking and while the engine is running, use a DC voltmeter and put the black meter lead on the battery POS (+) post and the red meter lead on the positive battery cable at the starter solenoid. Keep the black lead on the battery post and shift the red meter lead to the positive post of the rectifier, then to the red and white terminals on the switch box. If you find a reading above 0.6V, there is a problem at the point where the voltage jumped up. For example, if the meter reads 0.4V until you get to the white terminal and then jumps to 2.3V on the white terminal –this indicates a problem in the key switch, or harness. Repeat the test for the negative battery post by putting the black meter lead on the battery NEG (-) post and the red meter lead on the negative battery cable terminal, then shifting to the engine block, rectifier base and case ground of the CD module.


  • 1.

    Connect a spark gap tester to the high-tension lead coming from the ignition coil and set it to approximately 7/16”. When you crank the engine over, if it fires while the spark gap tester is connected to the coil and does not fire through the spark plug wires – there is a problem in the distributor cap, rotor button or spark plug wires.

  • 2.

    Check the DC voltage present on the white and red terminals while at cranking. It MUST be at least 9½ volts. If not, there is a problem in the harness, key switch, starter battery cables or battery.

  • 3.

    Check the DC voltage on the white/black trigger terminal while cranking, there must be at least 9V available with the trigger wire connected.

  • 4.

    Check DVA voltage between the blue and black trigger wires (they must be connected to the switch box). You should read at least 3V. A low reading indicates a bad trigger.

  • 5.

    Check DVA voltage on the green wire going to the coil, it should be over 100 volts at cranking.

ONLY HAS SPARK AS LONG AS THE STARTER IS ENGAGED: This symptom usually indicates a bad trigger or low voltage.


  • 1.

    Connect a spark gap tester to the high-tension leads coming from the distributor cap and set the gap to approximately 7/16”. Use of a CD Tester is highly recommended.

  • 2.

    Align the rotor with #1 spark plug wire. Disconnect the trigger wires and connect a jumper wire from the white/black trigger terminal to the black trigger terminal on the switch box.

  • 3.

    Connect another jumper wire to the blue trigger terminal turn the ignition switch on. Strike the jumper wire from the blue terminal against engine ground – (DO NOT HOLD THE JUMPER AGAINST ENGINE GROUND). Only the #1 spark plug wire should fire. If any other spark plug wire now has fire, there is a problem in the distributor cap.

  • 4.

    Repeat the test for the other cylinders.


Mercury Troubleshooting

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