Alternator Common Issues and Tips

Date Posted:3 December 2017 

Must Read Before Installing/Replacing Your Alternator


Some facts:

  1. 67% of all alternator failure is due to a faulty or weak battery;
  2. 14% of all alternator failure is due to poor electrical connections, fusable links, bad battery cables and bad grounds. (Voltage drop across the cables should not exceed 0.5V).
  3. 9% of all alternator failure is due to belt wear or improper adjustment – check for cracks, polished wear on belts and proper tension on belts.
  4. 6% of all alternator failure is due to jump starting another car improperly – failure to disconnect connection on alternator may cause voltage spikes.


  1. Before installing alternator, you must be certain of a fully charge battery.

    If your battery is not fully charged, charge it independently before fitting a new alternator.

    Do not fit a new alternator and expect it to than act as a battery charger.

    This is not the job of the alternator and will void your warranty.

    A battery charger must be used to charge your battery before you fit a new alternator.




    12.6V 100%
    12.4V 75%
    12.2V 50% 
    12.0V  25% 
    11.8V  0% 


  1. Never remove battery cable from battery to check charging system. This will cause damage to the alternator and computer system.

    When checking charge rate, bring engine RPM to 1500 and test voltage at rear of alternator. This should be between 13.8V and 14.4V. (Some computer controlled units may drop as low as 13V and as high as 14.7V).

    Repeat above test at battery. Voltage drop should be no less than 0.5 of a volt. If this is higher see an Auto Electrician to trace the voltage drop.

    Test maximum output. With volt meter at battery, turn all accessories on, bring to 2000 RPM and ensure voltage remains above 13V.


  1. Vacuum Pump Alternators

    Failure of Vacuum Pump Alternators is often caused by dirty oil in the vehicle. Please check for clean oil before fitting this unit.

    Always lubricate the vanes in the vacuum pump before fitting unit.

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