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The Zener diode is mounted within the electrical box at the front. Providing the diode is kept clean, to ensure maximum efficiency, no maintenance will be necessary. The "earthing" stud which secures the diode must not be subjected to a tightening torque greater than 24 - 28 lb./in. The electrical box lid acts as a heat sink and it is most important that the diode makes good contact with the mounting surface.
Checking performance of the Zener Diode
The battery should be fully charged before starting. If there is any doubt about the state of charge of the battery, it should be recharged before commencing the test. Isolate the Zener Diode by disconnecting all leads from the 2MC capacitor. Connect a D.C. voltmeter Black lead to the straight Lucar with the Brown/Blue cable and the voltmeter Red lead to earth. Connect a D.C. ammeter Red lead to the straight Lucar with the Brown/Blue cable, and the Black lead to the right angle Lucar with a Brown/Blue cable. Check that all electrical equipment other than the ignition is switched off. Start the engine and raise r.p.m. to approximately 3.000. Take a careful note of the readings. As the system voltage rises to 12.75 volts no reading should occur on the ammeter. The voltage will then continue to rise and after 12.75 volts the ammeter should start to read. The next check occurs when the ammeter rises to 2 amps, at this point the voltmeter should read between 13.5 and 15.5 volts.
Conclusions
The Zener Diode must be replaced if:-
(1) Current flow commences before 12.75 V is reached.
(2) Voltmeter registers more than 15.5 V. before 2 amps is shown on the ammeter.