How to Test an Alternator

Your vehicle's alternator is a vital component because it assists in charging your battery. Test your alternator to make sure your battery will continue to charge.

Instructions

  • Step 1: Find the battery Locate your car's battery, usually located on the left side of the engine if you're facing the front of the car. If it's not there, check the right side. Some cars even have their batteries under a seat in the middle of the car.
  • TIP: Consult the owner's manual for your vehicle if you can't find the battery.
  • Step 2: Connect at the voltmeter Connect the voltmeter to the battery while the car is off. Connect the red positive wire on the meter to the positive battery terminal, and connect the black wire on the meter to a bare metal grounding source, such as a nut or bolt on your car's frame.
  • Step 3: Read the battery's voltage Read the voltage on the meter to determine how many volts your battery is producing. Twelve is average, and if goes much lower than 11, you need a replacement.
  • Step 4: Turn the engine on Disconnect all wires and turn the engine on and reconnect the meter to the battery.
  • Step 5: Read the voltage Read the voltage on the meter as the car is running. If the voltage with the car running is higher than the voltage when the engine is off, then the alternator is fine. If it's lower, your alternator needs to be repaired or replaced.
  • FACT: Americans buy almost 3 billion dry-cell batteries every year.

You Will Need

  • Car battery
  • Car
  • Voltmeter
  • Owner's manual (optional)

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