I have a 2002 4.0L 4x4 Ranger with a charging issue. I bought a new battery as it was old and dead. Ran fine for several years but just finally wouldn't hold much of a charge. I took the old battery out and put the new one in and the battery light is on with the voltage meter 1/4 way (normally 1/2).

I bought a new alternator since I was only getting about 12V at the battery while running at idle (12.6 engine off). The new alternator also has the same issue...Battery light on, low voltage on gauge, and about 12V at the battery and the alternator B+ terminal while running.

Ive done extensive testing and know that the fusible link is good by a continuity test and voltage test, fuse number 11 7.5 amps (i think...the one that runs the instrument cluster lights. Im typing this from memory) is good. Ive also disconnected the three prong connector to the voltage reg on the alternator and tested the Y/W wire (A terminal) for voltage and it is about 11.5V - 12V with the key OFF (GOOD). I also tested the light green and red wire (terminal I) to ensure 0V with key OFF and is 12.4V (battery voltage) with key ON but engine OFF and this tested good too (actually it was about .2V less than battery voltage).

I then inspected the wiring as good as I possibly could being that it is ran through tight spaces but everything seemed ok. Nothing frayed or loose. I disconnected the ground at the starter, wire brushed it, added dielectric grease and reinstalled. That is the only ground that I found in the alternator circuit besides the small ground from the battery o the chassis. I even replaced the negative battery terminal since the old one was rusty (i didn't do the positive because the truck starts just fine so its getting power).

There is also a 50 amp fuse under the hood in the driver side fuse box that goes to the starter that I tested and this is good as well.

After all of this the light is still on and the alternator is only outputting about 12V while running. Ive tested this voltage at both the battery and the alternator output post itself (B+)...same results. The belt "seems" tight as well.

Can anyone help me figure out whats going on here. The alternator is brand new, not a remanufactured one. It is a Bosch which should be a reliable brand.

What would cause the alternator to read low voltage at the alternator post itself? Could it be a bad ground? Is shouldn't be a bad wire from the 3 pin connector because I'm getting voltage as expected. I tested 2 fuses with a continuity test and it passed...

Thanks in advance for any help!

 

Nice testing.

I would say that you've got a short somewhere, if both alternators are doing the same thing and with all you've tested.

I can't really suggest where else to go, but a short is more likely in my mind, any custom wiring on this? anything added?

 

Engine and key off
You test B+ wire on alternator, larger wire, should have Battery Voltage, in this case 12.x volts
Yellow wire on 3 wire connector should have the same
If not then bad fuse or fusible link

Light green wire on 3 wire connector should read battery voltage with key on, this is the ON/OFF switch for alternator.

Also on the 3 wire connector is a white jumper wire, make sure it is not frayed and gets plugged into separate alternator plug

Start engine, battery voltage should now be 14+ volts for the first few minutes

If you are reading just the 12volts then alternator is bad, new or not, it is not working

"New" used to mean "tested and working"
"New" now means, "YOU test it and we will replace it if it doesn't work"

 

there is a remote start installed (aftermarket installed by previous owner). Would something of this nature cause a short in the alternator circuit? I've gotten down under the dash and see where it's spliced into some factory wiring but am hesitant to mess with it since I don't know which wire does what. Could this be the issue?

 

Hi plus one to what RonD said, I would pay close attention to the fusible link RonD mentioned.

The one that caused me and a few Ranger owners that I know of problems is bundled near the positive battery cable.

You will have three of them they should be taped in such a way where you will just see the three wires looped.

The Smaller of the three wires which I think is brownish in color was broke in two on my truck and a few other memebers trucks.

A poorly installed aftermarket alarm can cause many problems yet I have yet to see one cause a short which resulted in a alternator to get burnt up or not allow it to charge.

Keep it simple check the fusible links if they are all good grab a Digital volt ohm meter and perform the test RonD mentioned.

 

I did more testing today with a buddy and am still just lost. I didn't check the 3 individual fusible links as they are all wrapped in the wire loom and didn't want to get into that just yet because everything tells me they're "okay". I did a test from the B+ to the negative terminal and got battery voltage (12.4) which tells me the fusible links are good. Just to confirm i did a continuity test from the B+ terminal on the alternator to the positive battery terminal and it passed showing continuity meaning in my mind that the fuse is good.

The additional testing is what got me a bit confused and I'm hoping someone here can help me. PLEASE NOTE that i did the following tests with the 3 wire harness disconnected from the alternator.

We measured voltage to the yellow wire which SHOULD be battery voltage BUT it is 2V shy showing 10V. IF this is a cable with a fusible link (not sure), it should either be 0V or 12.xV right (depending on fuse condition)? Why is it 2V shy of battery voltage?

Ok, now for more testing and more confusion...We then tested the light green wire once again and found what we expected which was 0V with key OFF and 12.xV with the key ON (engine off).

NOW, we removed the rubber on the back end of the 3 wire harness so we could easily access the pins from the backside while the plug was installed. We then installed the plug onto the alternator and tested these voltages again. The yellow wire is reading 5V with the key off (half of the 10V measured with the harness unplugged). We then read the green wire with the harness installed to the alternator and key ON and it measured 1.1V????? Why are these voltages not reading the same as when its unplugged? Does the voltage regulator step down the voltage?

I installed the old alternator and am returning the new one (bought it on amazon). I really feel something strange beyond a bad alternator is going on but I just don't know where to look anymore. Could one of the 3 fusible links be bad and still allow 12.xV at the B+ post?

One last thing I did with the new alternator before uninstalling was rev it to about 4,000 rpm and read voltage at the B+ post....NOTHING. Still 12.xV...not even 0.1V change

any tips or recommendations?

 

Yes check the fusible links, they are very easy to access and test, mine was broken in two pices yet just a few corroded strands were still providing battery voltage just not the current needed.

Your truck is exactly the same age as mine and I am pretty sure will need to be addressed even if it does not fix the problem.

You have nothing to lose but 15 minutes of your time, you could even just grab the fusible link and tug on it if it falls apart in your hand replace it, if the insulation is intact and the wire will not pull apart easily it should be fine.

Heck with mine I was able to cut the wire back a little to where the link wasn't corroded and resolder it back together.

 

could you guide me to the approximate location? Inside the loom 6" from positive terminal? 18"? I just want a better idea so I'm not risking accidentally cutting any wires while cutting the loom.

thanks!

 

You have a problem on the Yellow wire, it is also a direct connection to the battery same as B+ wire, so should show Battery Voltage

Yellow wire also uses a fusible link in your year.
All alternator fusible links will be together next to engine bay fuse box, it's positive battery cable connection terminal

The alternator's Green wire connection is a Ground when alternator is not spinning or making power.
That's what Battery Light is for, tells you if alternator is making power or is a Ground
When you turn on the key you are sending 12volts from cab fuse to dash battery light bulb, then out the green wire to alternator.

When you give a light bulb 12volts what happens..............nothing
When you give it 12volts AND a Ground it lights up
What if you give it 12volts on BOTH wires, what happens..........nothing

If alternator is producing power, 14volts, then green wire has 14volts, no longer a ground, and fuse in cab has 14volts, so Battery light is off
Battery Light on means alternator is a Ground


technically the you don't need the long yellow wire back to the engine fuse box, you could use a shorter wire with inline fuse or fusible link to the B+ terminal on alternator, and on many alternators thats what they do, just a jumper wire like the White wire

One wire alternators just have the B+ wire, yellow and green are BOTH connected to B+, usually internally.
But they must have an RPM switch inside or they will drain the battery
As alternator RPMs get above a set RPM the Green wire is powered, that powers up voltage regulator and Rotor, alternator then turns on and makes power
When RPMs drop below set level then power is cut to green wire and alternator shuts off so won't drain the battery.
An alternator IS an electric motor, not a good one as a motor, lol, but will spin if you give it power, which is why it will drain the battery if not turned off, it will try to turn fan belt, if power is left on, and of course not succeed, lol.

 

RonD, thanks for the explanation, EA outlaw thanks for pointing out the importance of this fusible link!!! I'll check tomorrow and reply back

 

Also I didn't mention it but yes, you test yellow and green wire voltages with 3 wire connector removed from alternator.
And use the alternator's case as the ground for the Volt meter, because thats what the alternator does.
You can test to battery negative as well just to make sure there is no difference, because there shouldn't be.

 

The positive cable on the battery goes down the side of the battery and enters a wire loom the llinks on my truck were right at that point and exposed they should not be covered or hidden in the loom if they have not been tampered with.

My truck with a 2.3 liter engine has two small air accumulators attached to the snorkel air inlet tube that made accessing these links a little difficult with the snorkel still attached.

Your truck has the 4.0 so I do not know for sure where your links are located.

RonD seems to know much more about the specifics about many Ford Rangers so I would advise going with his suggestions and advice if you cannot easily find these links where I found them on my truck.

Again the links should not be hidden they should be in plain sight and easy to get to with minimal work.

 

Problem solved! It was the yellow wire that was reading only 10V instead of 12.xV and I'm assuming the fusible link failed? I found the links you spoke of...right in plain sight, I just overlooked them because I was focusing so much on the ground connections because the alternator B+ was reading battery voltage so I figured the positive side of the circuit was good.

I looked at the wiring and couldn't see any noticeable damage at all (no burns, frays, etc...) I cut the wire out so I could inspect further and still didn't see anything odd even after removing all of the factory heat shrink. But I did what Ron said and ran a jumper from B+ to the yellow wire in the plug (after i cut and eliminated the voltage coming from the battery at the fusible link). Tested it, saw the correct voltage instead of the 10V like before and fired the truck up. Success!

Since the wiring is in such a tight area I think i will just by a 16ga fusible link and wire it in as a permanent jumper from the plug to the B+.

Thanks for all of the help and I really help this thread will help others. I looked everywhere on google, through many different forums and got pretty far, just not to my answer. I figured I'd better post my issues and sure enough, you guys helped me tons! Saved me $150 too!

 

Good work

That was an odd one

Thanks for posting the fix

 

The yellow and white wire in my diagram gets fed power from the brown Fusible link that fusible link gets power from one of the larger grey fusible links. ( again I am not sure if my diagram is the same as your truck since there is a engine difference).

What voltage are you getting from the brown fusible link?

If you are getting good battery voltage readings from it even when wiggling the links then you know the issue is with the yellow and white wire, but what you do not know is if the wire in question has interacted with another circuit from being pinched shorted etc.

Just being **** I would not stop diagnosing this problem until I knew for sure what exactly is the issue. Which could just be a bad connector at the alternator.

Right now even know you have a positive result you only have part of the story not knowing the rest could lead to an further reliability issues.

 

Necrobump but, if green wire with key on is reading 0v, where should I be looking next? Thank you

 

Welcome to the forum

You should start your own thread
Also always include the year of the Ranger, lots of differences by year
2002 Ranger, check fuse 11 in the cab fuse box, it powers Battery Light--------------green wire------------alternator