How to Check a Ford Alternator

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The alternator on your Ford is an electrical generator that recharges the battery while the car is on to power the ignition and electrical systems. When the alternator fails, the vehicle will shut off because the ignition system ceases to obtain a sufficient amount of electrical current to keep the engine running. But there could be another issue causing the problem you are encountering. So instead of replacing the alternator before knowing if it's actually bad, try diagnosing it with an electrical multimeter.

Things You'll Need

  • Eye protection
  • Digital multimeter
  • Start the engine of the Ford.

  • Open the hood and prop it up.

  • Place the dial of the digital multimeter on the DC volts setting; the alternator puts out electricity in direct current as opposed to alternating current.

  • Touch the negative lead of the multimeter on the negative terminal of the battery or to any engine ground that you can find. A ground is simply a metal component on the car that is used as an electrical pathway. The negative terminal will be indicated by a negative symbol, and the cable leading to it will be black.

  • Touch the positive lead of the multimeter to the nut holding the electrical cable routed to the alternator. The cable is typically red and large in diameter and is used to route the electricity generated in the alternator to the battery to recharge it.

  • Read the multimeter display. It should read at least 13.7-14.7V. If you read anything less than that, then there is an issue with the alternator, and it may have to be replaced.

  • Check the electrical connector attached to the alternator and make sure that it is pushed into the alternator firmly. This electrical connector provides electricity to the field windings in the alternator and is required for it to work properly. There should be 12V at the connector; this can also be checked with the multimeter.

  • Push down on the tab of the connector and pull out.

  • Place the black lead of the multimeter on the negative terminal of the battery. The negative terminal will be marked with a negative symbol and will have a black cable attached to it.

  • Place the positive lead in the pin of the connector that supplies power to the alternator. There will be three pins in the connector; the pin that you need to probe with the multimeter is the pin with a red wire leading to it.

  • Read the voltage on the multimeter. It should read 12V. If you are getting 12 volts, and the alternator isn't putting out between 13.7 and 14.7V, then the alternator is bad and needs to be replaced. If the connector you just checked isn't putting out 12V, then the alternator is most likely good, and the issue lies in the electrical wiring.

Tips & Warnings

  • If you don't have access to a multimeter or don't feel comfortable dealing with electricity, remove the alternator from the Ford and take it to an auto parts store where they can bench-test it for you.
  • Watch your hands, while checking the alternator, because the engine will be on. The alternator belt will be spinning at approximately 800 RPMs and can easily injure you. The radiator fans may also be on while checking the alternator or may turn on while working. To avoid losing a limb, be cognizant of where your hands are at all times.
  • Wear safety glasses to protect your eyes from injury.

References

  • "Automotive Repair and Rebuilding;" Jeffrey J. Rehkopf; 2006
  • Photo Credit Jupiterimages/Comstock/Getty Images
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