Need help with troubleshooting/repair of alternator system

[MagicalSavant77]

Hello all,
I picked up an '01 ranger xlt 4wd with the 4.0L. We're currently having issues with it not charging while running.

It's a relatively new battery (mfg date 7/25) and the alternator has tested good at the parts store. After charging the battery, I've been doing some multimeter testing and found that I'm getting battery voltage at the B+ post all the time (good), not getting battery voltage on the yellow wire at the plug for the alternator, and no voltage on the green wire with key in the off position, and battery voltage with it in run.

I'm not real sure where to go from here and would appreciate some help and advice. TIA for any help.

 

[2011Supercab]

RonD's alternator testing method

Alternator has 3 wires you need to test
B+ is the stud/nut terminal on the back of the alternator
As said above use the alternators metal case as the ground for all tests
Key OFF
B+ should show Battery Volts, leave wire attached, exactly the same as battery volts
If not then a fuse or fusible link is bad
This is the Voltage OUT to Battery positive so has a fuse at battery end of wiring

Unplug the 2 or 3 wire connector on alternator
Test the Yellow/White wire, should also show Battery volts, exactly
If not a fuse in engine bay fuse box is blown
This is the Voltage regulator's Monitor wire, tells the VR the alternator's output voltage to vehicle, so when you turn on headlights, for example, it sees the voltage drop and increases alternator's output voltage

Test the Green/Red wire, should be 0 volts
Turn the key ON
Re-test greed/red wire should now be 12volts, can be slight less than battery volts
This is the battery light wire, also the ON/OFF switch for alternator/voltage regulator
If this wire was grounded in the harness or in the dash area then battery light would come on but no alternator

If there is a 3rd White jumper wire then make sure it is plugged into the single spade terminal in the back of alternator, it can go in above or below the terminal so no connection and no alternator voltage

If the 3 wires voltages test as OK, and no charging after start up then alternator is bad, period, new or not

copied from here

Post in thread 'Replaced VR and then Alternator - still no charge'

Mar 20, 2024

+1 ^^^

Alternator has 3 wires you need to test
B+ is the stud/nut terminal on the back of the alternator
As said above use the alternators metal case as the ground for all tests
Key OFF
B+ should show Battery Volts, leave wire attached, exactly the same as battery volts
If not then a fuse or fusible link is bad
This is the Voltage OUT to Battery positive so has a fuse at battery end of wiring

Unplug the 2 or 3 wire connector on alternator
Test the Yellow/White wire, should also show Battery volts, exactly
If not a fuse in engine bay fuse box is blown
This is the Voltage regulator's...

• RonD

• 

 

[MagicalSavant77]

That's exactly what I followed and I'm not seeing the correct voltage from the yellow wire. I'm just not sure what that means or how to fix it.