TEST 2: Making Sure The Alternator's Battery Circuit Has Continuity
In the illustration above I have highlighted the circuit that delivers the alternator's current output to the battery.
The current output starts at terminal B+ (arrow B+) on the back of the alternator and passes thru the 175 mega fuse (arrow F) and finally reaches the battery positive (+) terminal.
You can find the complete alternator circuit wiring diagram here: Alternator Circuit Diagram (1998-2001 2.5L Ford Ranger).
Let's get testing:
- 1
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. - 2
Place your multimeter in Ohms mode.
- 3
Connect the black multimeter test lead to the center of the battery positive post.
- 4
Connect the red multimeter test lead to the stud on the rear of the alternator.
- 5
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: Continuity is present in the circuit. This is the correct test result and let's you know that the 175 mega fuse is OK and not blown.
The next step is to make sure that your alternator's voltage regulator is getting power. For this test go to: TEST 3: Making Sure The Alternator's Voltage Regulator Is Getting 12 Volts.
CASE 2: Continuity IS NOT present in the circuit. This test result usually means that the 175 mega fuse is blown.
TEST 3: Making Sure The Alternator's Voltage Regulator Is Getting 12 Volts
If you've reached this point, you have confirmed that:
- Your 2.5L Ford Ranger's alternator is not charging the battery (TEST 1).
- That the circuit (wire) that delivers the alternator's current output to the battery has continuity (TEST 2).
In this test section, we are now going to check that the voltage regulator on your 2.5L Ford Ranger's alternator is getting battery power.
This battery power reaches the voltage regulator across the yellow with white stripe (YEL/WHT) wire of the 3-wire connector connecting to it.
In the illustration above I have highlighted the circuit that delivers these 10 to 12 Volts to the alternator's voltage regulator.
Let's get testing:
- 1
Unplug the alternator voltage regulator from its 3-wire electrical connector. You'll find the voltage regulator bolted to the rear of the alternator.
- 2
Place your multimeter in Volts DC mode..
- 3
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 multimeter's test leads 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 interpret your multimeter voltage test result:
CASE 1: Battery power is present in the YEL/WHT wire. This is the correct test and lets you know that the 30 Amp alternator fuse in your 2.5L Ford Ranger's under hood fuse box is not blown and that the voltage regulator is getting battery power.
You can conclude that the alternator is defective and needs to be replaced if you have:
- Confirmed that the alternator is not charging the battery (TEST 1).
- Confirmed that the wire (circuit) that delivers the alternator's current output to the battery has continuity (TEST 2).
- Confirmed that the voltage regulator is getting battery power.
CASE 2: Battery power IS NOT present in the YEL/WHT wire. This usually means that the 30 Amp alternator fuse in the under-hood fuse box is blown. Your next step is to check the fuse, replace it if it's blown and retest.
