ALTERNATOR TEST 2

How To Test A Bad Alternator (Ford 3.0L, 3.8L)

The alternator's charging output is delivered to the battery across one main wire. This is the large wire that is attached with a nut to the one and only stud behind the alternator (see photos in the image viewer).

On older Ford 3.0L and 3.8L vehicles, an inline fusible link is used to protect this wire (circuit). On the newer ones, a plastic fuse is used.

If this fuse or inline fusible link is blown, the alternator could be working, but the charging output will never reach the Battery. So, in this test, you're gonna' verify that this inline fusible link (or fuse) is not blown by doing a simple resistance (Ohms) test with your multimeter.

Let's get going:

  1. 1

    This test has to be done with the battery negative (-) cable disconnected from the battery. This is important, do not proceed beyond this point without first disconnecting the battery negative cable. The battery positive cable must remain connected to the battery.

  2. 2

    After disconnecting the battery negative (-) cable, turn on your multimeter and select Ohms mode.

  3. 3

    Now, place the red multimeter test lead on the center of the stud to which the large wire is attached to with a nut. You can see what this stud looks like by checking out the photos in the image viewer.

  4. 4

    With the black multimeter test lead, probe the center of the battery positive post on the battery.

  5. 5

    You'll see one of two results on your multimeter:

    1.) If the inline fusible link (or fuse) protecting this circuit is blown, your multimeter will indicate a reading of OL (which means over limit).

    2.) If the inline fusible link (or fuse) is OK and not blown, your multimeter will register an Ohms reading of 0.5 Ohms or less.

OK, now that the testing part is done, let's take a look at what your results mean:

CASE 1: Your multimeter registered 0.5 Ohms. This is good, since it indicates that the inline fusible link or fuse is OK and not blown.

The last test to do, is to verify that the alternator's voltage regulator is getting 12 Volts. These 12 Volts are provided through a regular plastic blade type fuse. OK, for this test go to: TEST 3.

CASE 2: Your multimeter DID NOT registered 0.5 Ohms, it registered OL. This result tells you that the inline fusible link is blown.

Replace the fuse and retest. Replacing this blown inline fusible link or fuse should solve your no charge condition. You'll have to investigate the reason this inline fusible link or fuse blew, since they don't go bad for no particular reason.

You're probably wondering: So where's this inline fusible link or fuse located at? Well, it's beyond the scope of this article to tell you (since it covers so many Ford, Mercury and Lincoln vehicles). You'll need a repair manual or a Google Search for it but I can tell you that they are always located in the engine compartment and usually connects to the Engine Compartment Fuse Box.

Ford Vehicles:

  • Aerostar 3.0L
    • 1992, 1993, 1994, 1995, 1996, 1997
  • Mustang 3.8L
    • 1997, 1998, 1999, 2000, 2001, 2004
  • Probe 3.0L
    • 1990, 1991, 1992
  • Ranger 3.0L
    • 1991, 1992, 1993, 1994, 1995, 1996, 1997

Ford Vehicles:

  • Taurus 3.0L, 3.8L
    • 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
  • Tempo 3.0L
    • 1992, 1993, 1994
  • Thunderbird 3.8L
    • 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997

Lincoln Vehicles:

  • Windstar 3.0L, 3.8L
    • 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003

Lincoln Vehicles:

  • Continental 3.8L
    • 1989, 1990, 1991, 1992, 1993, 1994

Mercury Vehicles:

  • Cougar 3.8L
    • 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997
  • Sable 3.0L, 3.8L
    • 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005
  • Topaz 3.0L
    • 1992, 1993, 1994

Mazda Vehicles:

  • B3000 3.0L
    • 1994, 1995, 1996, 1997