How to Test a BAD  Alternator (Ford 3.0L, 3.8L)

This article will help you to test and troubleshoot a No Charge Condition on any Ford (and Mercury and Lincoln) 3.0L and 3.8L V6 equipped car, pick up or mini-van.

The only piece of diagnostic/testing equipment you'll need to test the alternator and to follow the step-by-step instructions, is a multimeter (doesn't matter if it's a digital or analog multimeter).

If you need to see if this alternator test article applies to your specific Ford vehicle... on the column on the right, you'll see a container with the heading ‘Applies To:’ that will have a list of Ford, Mercury, and Lincoln vehicles this article applies to.

Here are the contents of this article at a quick glance:

  4. Symptoms of a BAD Alternator.
  5. Related Test Articles.


This is an On-Car test of your Ford's alternator. This first test is done with the engine running, so you have to be careful, alert, and take all necessary safety precautions.

The most important part of this first alternator test is that you need to make sure that the battery is fully charged before starting this test, since you'll need to have the engine running for the duration of this first test.

Well, without further ado, this is what you need to do:

  1. 1

    Start the engine and place your multimeter in Volts DC mode. Again, be careful, since you'll be working around a running engine.

  2. 2

    Place the RED multimeter test lead on the battery positive terminal and the BLACK multimeter test lead on the battery negative terminal.

  3. 3

    Your multimeter will register one of two things (depending if it's charging the battery or not). It will either:

    1.) Show a steady DC Volts reading of about 13.5 to 14.5 Volts the whole time the engine is running or

    2.) Show a voltage of about 12.5 Volts that decreases the longer the engine is running.

  4. 4

    The next step is to have an assistant turn on everything and anything that uses electricity inside the vehicle like: headlights, windshield wipers, turn signals, a/c or heater blower on high, etc.

    This will put an electrical load on the alternator to either confirm it's really working or it's fried.

  5. 5

    Observe the multimeter's readings, since your multimeter will react to the things that are turned on (if it's BAD). OK, here's what is going to happen...

    The multimeter's reading will continue to drop down to about 9 Volts or more (the vehicle may stall around 9 Volts) or the voltage reading will stay steady around 13.5 to 14.5 Volts the whole time.

Take a look at the following test interpretations to find out which one best fits your multimeter test results:

CASE 1: If your multimeter registered 13.5 to 14.5 Volts. This indicates that the alternator IS working fine and charging the battery.

So then, this multimeter test result eliminates the alternator as BAD on your Ford 3.0L or 3.8L equipped car, pick up or mini-van.

CASE 2: If your multimeter registered a voltage that steadily dropped down to 9 Volts: This indicates that the alternator is NOT charging the battery.

You could replace the alternator now, with just this test result... and about 90% of the time, the No Charge Condition would be solved. To be absolutely sure the alternator is really fried on your vehicle, I recommend to do two more important (but easy) tests. Go to ALTERNATOR TEST 2.