TEST 2: Testing The Continuity Of The Battery Circuit
The current that the alternator produces to recharge the battery is transmitted to the battery across a single wire. This wire connects to the rear of the alternator through a stud.
Before this cable reaches the battery, it goes through a 10 gauge inline fusible link. And every now and then this inline fusible link get blown. So in this test section we're gonna' do a simple continuity test on this circuit (to make sure that the inline fusible link is not blown).
IMPORTANT: Before you perform this test it's important that you disconnect the battery negative (-) cable from the negative battery post.
NOTE: You don't have to remove the alternator to do this continuity test. The illustration above shows the alternator off the vehicle just for facilitating the explanation of the multimeter probe test connections.
Here are the test steps:
Disconnect the battery negative (-) terminal from the battery negative post. Leave the positive cable connected to the positive post.
IMPORTANT: Don't proceed to the next step without first disconnecting the battery from its negative cable.
Place your multimeter in Ohms mode.
Connect the black multimeter test lead to the center of the battery positive post.
Connect the red multimeter test lead to the stud on the rear of the alternator. The orange arrow, in the illustration above, points to this stud on the Ford Taurus (o Mercury Sable) alternator.
You'll see one of two results: The multimeter will register continuity or it won't.
If the multimeter register's continuity, you'll usually see 0.5 Ohms. If it registers no continuity, you'll see the letters OL displayed.
Let's interpret your multimeter continuity test result:
CASE 1: Your multimeter registered continuity in the circuit. This is the correct test result.
Now there's one more test to do and this is to make sure that the alternator;s voltage regulator is being fed 10 to 12 Volts DC. For this test go to: TEST 3: Making Sure The Voltage Regulator Is Getting 12 Volts.
CASE 2: Your multimeter indicates that the circuit does not have continuity. This test result usually means that the inline fusible link (that protects this wire) is blown. If this inline fusible link is blown, the alternator's current will not reach the battery.
Your next step is to check that this 10 gauge inline fusible link okay. If the 10 gauge inline fusible link is blown, replace it with another and return to and repeat TEST 1.
TEST 3: Making Sure The Voltage Regulator Is Getting 12 Volts
The alternator's voltage regulator needs to be fed 10 to 12 Volts so that it can activate the alternator.
If this voltage is missing, the alternator will not start charging the battery. So, and this test section, we're gonna' make sure that this voltage is present.
Let's get started:
Unplug the alternator voltage regulator from its electrical connector. This connector connect to the rear of the alternator and you can identify it with the illustration above.
Place your multimeter in Volts DC mode..
Verify that the terminal identified with the letter A has 10 to 12 Volts with the key on or the key off.
NOTE: Avoid probing the front of the terminal with your multimeters probe or you will damage it. You'll need to use a back-probe or a wire piercing probe to test for the presence of this voltage in the wire.
Let's find out what your test results mean:
CASE 1: Your multimeter registered 10 to 12 Volts. This is the correct test result and lets you know that the voltage regulator is getting the power it needs to activate the alternator.
You can correctly conclude that the alternator is defective if you have:
- Confirmed that battery voltage is at 12 Volts with the engine running (TEST 1). And that this voltage decreases the longer the engine stays running.
- Confirmed that battery circuit wire that connects to the rear of the alternator has continuity (TEST 2).
- Confirmed that the voltage regulator is getting 10 to 12 Volts (TEST 3).
CASE 2: The multimeter did not register 10 to 12 Volts. Without 10 to 12 Volts, the voltage regulator will not activate the alternator to start charging the battery.
The most common cause of this lack of power (to the alternator's voltage regulator) is usually due to a blown fusible link. This 18 gauge fusible link connects to the under hood fuse box in the engine compartment.
Your next step is to make sure that this 18 gauge inline fusible link is not blown. If the 18 gauge fusible link is blown, replace it and repeat TEST 1.
More 3.0L Ford Tutorials
You can find a complete list of 3.0L Ford tutorials in these two indexes:
Here's a sample of the tutorials you'll find in these indexes:
- How To Test The TPS -1994-1995 3.0L Ford Taurus.
- How To Test The Fuel Pump (1990-2000 3.0L Ford Taurus).
- How To Test The Crank Sensor (Ford 3.0L, 3.8L).
- How To Test For A Blown Head Gasket (Ford 3.0L, 3.8L).
If this info saved the day, buy me a beer!