How To Test The Alternator (1992-1993 Ford E150, E250, E350)

TEST 2: Testing The Continuity Of The Alternator's Output Wire

The alternator's voltage and amperage output reach the battery across a wire.

Inline fusible links protect this alternator output wire, and in some cases, these fusible links get blown.

We'll do a multimeter continuity test on the alternator's output wire to confirm that these fusible links are not blown.

NOTE: The fusible links that protect the alternator's battery output wire are located on the starter motor relay.

OK, these are the test steps:

1. 1

   Disconnect the battery negative (-) cable from the battery.
   
   IMPORTANT: Do not proceed to the next steps until you do this first.

2. 2

   Set your multimeter to Ohms mode.

3. 3

   Connect the red multimeter test lead to the stud shown in the photo above.
   
   The alternator's output wire connects to the stud the arrow points to (in the photo above).

4. 4

   Connect the black multimeter test lead on the battery positive (+) terminal (at the battery).
   
   The battery negative (-) wire must remain disconnected from the battery.

5. 5

   Your multimeter will register one of two values:
   
   1.) An Ohms value of about 0.5 Ohms.
   
   2.) An infinite Ohms reading (OL).

OK, let's take a look at what your results mean:

CASE 1: Your multimeter registered 0.5 Ohms. This is the correct and expected test result and it tells you that the fusible links that protect the alternator's output wire are OK.

So far, it's looking like the alternator is bad. The last test to make sure it is is also a very simple test and it involves checking a fuse only. For this test, go to: TEST 3: Checking The Alternator Fuse.

CASE 2: Your multimeter DID NOT register 0.5 Ohms, it registered OL. This test result confirms that the fusible links that protect this wire are blown.

Your next step is to replace the inline fusible links and retest.

TEST 3: Checking The Alternator Fuse

OK, for our last test, we'll test the alternator fuse. The alternator fuse on the 1992-1993 Ford E150 (E250, E350) is fuse #7 located in the interior fuse box (under-dash fuse box).

Let's get started:

1. 1

   Locate fuse #7 of the interior fuse panel.

2. 2

   Remove fuse #7 of the interior fuse panel.

3. 3

   Visually inspect the fuse.

4. 4

   You'll see one of two things:
   
   1.) The fuse is blown.
   
   2.) The fuse IS NOT blown.

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

CASE 1: The fuse is NOT blown. This is the correct and expected test result.

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

• Confirmed that battery voltage is below 12.5 Volts DC as the engine runs (TEST 1).
• Confirmed that the inline fuses that protect the alternator's output wire are not blown (TEST 2).
• In this test section, you've confirmed that the alternator fuse located in the interior fuse box is OK.

CASE 2: The fuse IS blown. Replace the fuse and check the battery voltage with the engine running. The alternator should be charging the battery.

If the alternator does not charge the battery, you can conclude that it's bad (and needs replacement) if you have:

• Confirmed that battery voltage is below 12.5 Volts DC as the engine runs (TEST 1).
• Confirmed that the inline fuses that protect the alternator's output wire are not blown (TEST 2).

More Ford E150, E250, And E350 Tutorials

You can find a complete list of tutorials for the full-size Ford E-Series vans here:

• Ford 4.9L, 5.0L, 5.9L Index Of Articles.

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

• Manifold Absolute Pressure MAP Sensor Test (Ford 4.9L, 5.0L, 5.8L).
• Ignition Coil Test -No Spark No Start Tests (Ford 4.9L, 5.0L, 5.8L).
• How To Troubleshoot A No Start (Ford 4.9L, 5.0L, 5.8L).
• Testing A Blown Head Gasket (Ford 4.9L, 5.0L, 5.8L).
• How To Test Engine Compression (4.9L, 5.0L, 5.8L).