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Alternator Testing


  • To prevent damage to the alternator (GEN), do not make jumper wire connections except as directed.
  • Do not allow any metal object to come in contact with the housing and the internal diode cooling fins with key on or off. A short circuit will result and burn out the diodes.
  • Battery posts and cable clamps must be clean and tight for accurate meter indications.
  1. Turn OFF all lamps and electrical components.
  2. Place the vehicle in transmission range NEUTRAL and apply the parking brake.
  3. Carry out the Load Test and No-Load Test.
  1. Switch the Battery Tester to the ammeter function.
  2. Connect the positive and negative leads of the Battery Tester to the corresponding battery terminals.
  3. Connect the current probe to the alternator B+ output lead.
  4. With the engine running at 2000 rpm alternator output should be greater than as shown on the graph.
  1. Switch the Battery Tester to the voltmeter function.
  2. Connect the voltmeter positive lead to the alternator B+ terminal and the negative lead to ground.
  3. Turn all electrical accessories off.
  4. With the engine running at 2,000 rpm, check the alternator output voltage. The voltage should be between 13.0 and 15.0 volts.

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