How To Test The Alternator (1998-2001 4.0L V6 Mercury Mountaineer)

TEST 2: Testing The Continuity Of The Alternator's Battery Circuit

In this test section, you'll test the continuity of the alternator's output wire.

This output wire delivers the alternator's voltage and amperage output to the battery.

This wire has a mega fuse or fusible links protecting it between the alternator and the battery.

The alternator's output will not reach the battery if this fuse is blown.

You'll do a simple continuity test with your multimeter to check the condition of the output wire's mega fuse or fusible links.

Let's get testing:

1. 1

   Disconnect the battery negative (-) terminal from the battery. Do not proceed to the next steps till you do this first.
   
   NOTE: Leave the battery positive (+) cable connected to the battery.

2. 2

   Set your multimeter to Ohms mode.

3. 3

   Connect the red multimeter test lead to the stud behind the alternator. This stud is where the big wire that supplies the alternator's output to the battery attaches to with a nut.
   
   The arrow in the photo above points to the stud location.

4. 4

   Connect the black multimeter test lead to the battery positive (+) terminal.

5. 5

   Your multimeter should register about 0.5 Ohms to 1 Ohms if the inline fusible link or mega fuse is not blown.
   
   If the output wire's inline fusible link or mega fuse is blown, your multimeter will register an infinite Ohms reading (OL).

Alright, let's interpret your test results:

CASE 1: Your multimeter registered continuity (0.5 to 1 Ohms). This is the correct and expected test result.

With this result, you can conclude that the output wire's inline fusible links or mega fuse is OK and not blown.

Your next step is to make sure the alternator's voltage regulator is receiving 12 Volts. For this test, go to: TEST 3: Making Sure The Voltage Regulator Is Receiving 12 Volts.

CASE 2: Your multimeter DID NOT register 0.5 to 1 Ohms, it registered OL. This result tells you that the inline fusible links or mega fuse is blown.

You'll need to replace the inline fusible link or mega fuse and re-test the battery's voltage with the engine running. This should solve your no-charge condition.

TEST 3: Making Sure The Voltage Regulator Is Receiving 12 Volts

The voltage regulator inside the alternator needs 12 Volts to activate the alternator to charge the battery.

If the voltage regulator doesn't receive these 12 Volts, the alternator will not charge the battery.

So in this test section, you'll check that the yellow with white stripe (YEL/WHT) wire (of the voltage regulator's connector) delivers these 12 Volts.

The YEL/WHT wire connects to the female terminal labeled with the letter A in photo 2 of 2 in the image viewer above.

These are the test steps:

1. 1

   Reconnect the battery to its battery negative (-) cable.

2. 2

   Disconnect the voltage regulator from its electrical connector.

3. 3

   Place your multimeter in Volts DC mode.

4. 4

   Connect the black multimeter test lead directly to the battery negative (-) terminal.

5. 5

   Probe the yellow with white stripe (YEL/WHT) wire of the alternator's voltage regulator connector with the red multimeter test lead.

6. 6

   Your multimeter should register one of two things:
   
   1.) 10 to 12 Volts DC, if the fuse (fusible link) is good.
   
   2.) 0 Volts DC, if the fuse (fusible link) is blown.

Let's take a look at what your specific test results mean:

CASE 1: The multimeter registered 10 to 12 Volts. This is the correct and expected test result and confirms that the voltage regulator is getting power.

You can conclude that the alternator is bad and needs replacement if you have:

• Confirmed that the battery voltage is NOT at 13.5 to 14.5 Volts DC with the engine running and all accessories turned on (TEST 1).
• Confirmed that the alternator's output wire has continuity (TEST 2).
• Confirmed, in this test section, that the YEL/WHT wire has 10 to 12 Volts.

CASE 2: The multimeter DID NOT register 10 to 12 Volts. Please replace the fuse or fusible link with another of the same amperage rating and repeat TEST 1.

More 4.0L Mercury Mountaineer Tutorials

You can find more 4.0L V6 Ford Explorer (Aerostar) diagnostic tutorials here:

• Ford 4.0L Index Of Articles.

Here's a sample of the tutorials you'll find in the index:

• How To Test For A Blown Head Gasket (Ford 4.0L Explorer, Aerostar And Mercury Mountaineer).
• How To Test The Fuel Pump (Ford 4.0L Explorer, Aerostar And Mercury Mountaineer).
• How To Test Engine Compression (1991-2010 4.0L Ford Explorer, Aerostar, And Mercury Mountaineer).