TEST 2: Checking The Continuity Of The Bat (+) Cable

How To Test The Alternator (2.8L S10 Blazer, 2.8L S10 Pick Up, 2.8L S15 Pickup, and 2.8L S15 Jimmy)

The next step is to make sure that the battery cable, that connects the battery positive terminal to the rear of the alternator, does not have an ‘open’.

In other words, we're gonna' make sure, with a continuity test, that this cable is really able to deliver all of the alternator's output to the battery.

IMPORTANT: This test involves disconnecting the battery negative cable from the battery negative terminal before testing this circuit with your multimeter in Ohms mode.

This is what you'll need to do:

  1. 1

    Disconnect the negative battery cable terminal from the battery negative post. The positive cable remains connected.

    IMPORTANT: Don't continue to the next step without first disconnecting the negative cable from the negative battery post.

  2. 2

    With the negative battery cable disconnected from the negative battery post, turn on your multimeter and select Ohms mode.

  3. 3

    Locate the stud that the battery current output wire connects to on the back of the alternator. This wire is attached with a nut to the stud. Place your multimeter's RED test lead on the stud to which this wire is connected to.

    The orange arrow in the photo above points to this stud.

  4. 4

    With the black multimeter test lead probe the center of the battery positive post on your S10/S15's battery.

  5. 5

    You'll get one of two results.

    1.) The multimeter WILL NOT register continuity and it will register the letters OL (which means over limit).

    2.) If the battery wire does have continuity, your multimeter will register an Ohms reading of 0.5 Ohms or less.

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

CASE 1: Your multimeter registered continuity: This is good, since it indicates that the entire circuit is OK and that if the alternator were charging the battery, this charge would actually reach the battery.

There's one more test to do. This one involves checking the condition of the IGN/GAUGES fuse inside your S10 (or S15). For this test, go to: TEST 3: Checking The Alternator Circuit Fuse.

CASE 2: Your multimeter DID NOT register continuity: This result tells you that the alternator's BATTERY wire has an open. This means that the alternator's charge is not reaching the battery.

On all of the S10 and S15s covered by this tutorial, this alternator battery wire connects directly to the battery positive cable/terminal. To be a bit more specific, there's no fusible link that attaches to this battery cable. So if your multimeter indicates this wire is open, you'll need to replace it with a new one and of the same gauge (thickness).

TEST 3: Checking The Alternator Circuit Fuse

Checking The Alternator Fuse on the Fuse Panel Located Under the Dash (2.8L S10 Blazer, 2.8L S10 Pick Up, 2.8L S15 Pickup, and 2.8L S15 Jimmy)

The fuse that you need to check and make sure IS NOT blown is the fuse labeled with the #4 in the illustration above. This fuse is labeled as the IGN/GAUGES fuse on the fuse panel.

The fuse panel is located under the driver-side dash next to the parking brake.

FUSE CHECK RESULT: If in TEST 1 the battery voltage (with the engine running) was below 12.5 Volts, in TEST 2 the battery output circuit has continuity and the #4 fuse is OK, then the alternator is defective and replacing it should solve the no charge condition.

Chevrolet Vehicles:

  • S10 Blazer 2.8L
    • 1988, 1989
  • S10 Pickup 2.8L
    • 1988, 1989, 1990, 1991 1992, 1993

GMC Vehicle:

  • S15 Jimmy 2.8L
    • 1986, 1987, 1988, 1989

GMC Vehicles:

  • S15 Pickup 2.8L
    • 1986, 1987, 1988, 1989, 1990