Ok guys, don't let me down. I've been banging my head against a wall for weeks trying to figure this out.

Long story short:

Vehicle: 2001 Ford Ranger 4.0L V6 XLT
Problem: Battery not charging, car sluggish upon acceleration

Quick intro:
1. Driving around and car died on the road. Tested the alternator and it said it was good, battery core was fried so replaced the battery.
2. On the road again, and same thing. This time I replaced both the alternator (from the 95amp to 130amp) and the battery.
3. On the road again, but this time sluggish acceleration, battery slowly draining.
4. Slow charged battery for 24 hrs, cleaned terminals etc. and installed: reads only 12.2V when car is running. I check the draw upon starting: battery drops below 10V. After running for some time with lights on etc. battery reads: 11.86V. So I check the alternator. Ground to B post: 11.86V, positive to B Post: 0.03V, ground to case: 0.65V.

Can someone tell me what is going on?? I haven't gotten the new alternator and battery tested because I made the assumption they were both good from O'Reillys.

 

Get out the volt meter again.

Yes, on the back of the alternator there is the B+ terminal(big wires and nut) and with key off it should read "battery voltage", if not then fuse/fusible link is blown.

Then there is a 2 or 3 wire connector on the alternator, unhook it.
Yellow wire should also show "battery voltage", if not fuse/fusible link is blown

Light Green wire, should show 0 volts, now turn on the key, this wire should now show "battery voltage", this is the ON/OFF switch for alternator, it is also the Battery Light wire, if battery light hasn't been coming on when you turn on the key then fuse in cab fuse panel is blown, and that's why you are not charging, usually 7.5amp fuse

If these all check out then alternator is bad, doesn't matter if it tests OK, it is bad.
On some there will also be a white jumper wire, it needs to be connected and wire checked, if it is hanging by a thread then fix it

Alternators are very simple devices, the internal voltage regulator feeds the rotor 7volts DC, and the 3 "fields"(in the case) generate AC volts as rotor spins past them
2 diodes on each Field convert AC to DC volts and that is sent to B+
7 Volts in will produce 14volts out, voltage regulator adjusts that 7 volts up and down to keep battery from over or under charging

Yellow wire powers the regulator and is the voltage "monitor", prevents over or under charging

Light Green wire turns off voltage to the Rotor so alternator doesn't drain battery when engine is off, this connection is a "ground" when alternator is not spinning.
This wire goes to one side of Battery Light in the dash, when you turn on the key the other wire on the Battery Light gets 12volts(battery voltage), since Light Green wire is a "ground" Battery Light comes on.
After engine starts(alternator is spinning) the Light Green wire is no longer a "ground" it has same voltage as the wire on the other side of Battery Light, equal voltage means Battery Light goes out, no voltage passing thru the bulbs filament.

An Alternator is basically an electric motor used in reverse, so if you left the power ON it would try to turn the engine via the fan belt, it of course couldn't but would drain the battery trying.


An alternator should produce just under 15volts at battery after starting, then after battery has been recharged from the drain of starter motor, voltage will drop to about 13.6volts, this is called a maintenance charge, it keeps battery charged but won't "cook it", boil off chemicals.
This change in voltage can take a few minutes , depends on the battery, but if it stays high then either battery is bad, or voltage regulator is, if it is the voltage regulator then battery WILL go bad, so you do need to watch for that.

 

OK

Battery Voltage (POS to NEG, engine OFF): 12.1V
B+ Terminal (to NEG, engine OFF): 12.07V

Does anyone know where the fuse/fusible link is? I've looked around my under-hood fuse box, no large fuses visible..

Yellow Wire (to NEG, engine OFF): 10.7V 11.4V
This is a bit jumpy...any ideas?

Light Green Wire (to NEG, engine OFF): 0.01V

Battery Voltage (POS to NEG, engine ON): 11.8V
Light Green Wire (to NEG, engine ON): 11.71V

I can pick up another alternator if needed, this one has a lifetime warranty.



Also, I thought it was worth mentioning I (accidentally) tested the top of the radiator to the NEG terminal and it showed -0.4V, what would this mean?

Thanks for all the help RON!!

 

The Fusible links for charging system all show they come from Battery Junction box.

Was the White wire OK?
Looks good

Yellow wire is troublesome, that is almost a 2 volt drop, thru a direct connection to battery.

On my 2001 diagram it show 2 fusible links(both Grey) in parallel for B+ wire(Black/orange wire)
And 1 fusible link(Brown) for the Yellow wire, but this is connected to B+ wire.

So B+ and Yellow wire should read exactly the same voltage at the alternator.

With meter connected to Yellow wire(disconnected from alternator) try moving the wiring harness around to see if you can find the bad connection.

Diagram here: | Repair Guides | Charging System (2001) | Charging System (2001) | AutoZone.com

 

Thanks for the diagram and info. I'll have to do some research and some more poking around. Does anyone have a video of how to move/remove the wiring harness for diagnostics?

 

Ok, so I tested a bit more (now that the weather is better), and came up with the following:

Battery Voltage (POS to NEG, engine OFF): 12.12V
Battery Voltage (POS to NEG, engine ON): 11.87V
B+ Terminal (to NEG, engine ON): 11.79V
Yellow Wire (to NEG, engine ON): 11.79V
White Wire (to NEG, engine ON): 0.09V

I replaced the "Left stop/turn trailer tow connector" fuse #7 at 7.5A as that was blown, though I don't think it's related. The battery light on the dash is on.

I moved the wiring harness around to see if there was any bad connection, and didn't find any yet. Same thing with the fusible links. Everything seems to check out.

THOUGHTS??!?!?

 

For sure the alternator is not putting out any power

Light green wire on 3 wire connector
Unplug connector
engine OFF, key ON

Red volt meter probe to Green wire, black probe to Ground(battery "-")
Needs to show 12.12v, or same as battery

If not fuse is blown in cab fuse box, usually 7.5 amp

All alternator voltages are tested with engine OFF, Key OFF except for this one wire.
Only voltage tested with engine running is battery voltage, over 13.5volts means alternator is working, under 13.5volts means it's not, so 11.79v is a not working

Take alternator back if possible.
new battery is also drained, should be 12.7v or higher

 

Ok,

Battery Voltage (POS to NEG, engine OFF, key ON): 11.98V
Light Green Wire (to NEG, engine OFF, key ON): 11.84V

All fuses (in cab and under hood) have been tested and the one mentioned above was replaced.

 

I took the alternator back, they tested it (fail) and the others they had in stock (fails), apparently they had a bad batch. Gave me remanufactured one that passed.

HOWEVER

Battery charged back to 12.7V
After install:
Battery Voltage (POS to NEG, engine ON): 11.79V

WTF!?!

 

Can you get your money back, this place is causing you a lot of wasted time and effort.
"We must have got a bad batch", now that's a WTF!

Charging systems are just not that complicated
You tested all the wires and they are good, so alternator is bad, not complicated at all
Maybe "bad" alternator blew a fuse..........
If you want to test wires again then do that:
engine OFF, key OFF
B+ wire = battery voltage
3 wire connector unplugged
yellow wire = battery voltage

Key ON, engine off
Green wire = battery voltage

If wires pass the test then plug connector back in and start engine
Battery voltage above 13.5v all is well
Battery voltage below 13.5v alternator is bad

Read here: Ford Ranger Alternators

get one from a wrecking yard, plug n' play

 

I have searched all over internet for the fuseable link. Apparently on 2000 ford ranger 3.0 doesn't have one it's call a mega fuse hooks right to outside of fuse box under hood, that has been my problem for alternator not putting out enough volts. But thank you everyone that wrote on this i now understand how an alternator works and what wire does what and where.

 

You left future members searching, hanging out to dry?
What brand alternator was bad?
I assume you fixed it, as too many who fix something, never bother to come back & say " This fixed it!"

 

I’ve did all the checks, my green wire does not have voltage with key on. / battery light is not coming on, on dash. From reading in this thread, that tells me I have a blown fuse in my cab. 7.5amp. But I’ve checked all my fuse twice and they all look good. Do you happen to know what number/location or what they call the fuse.
thanks

 

can’t find the fuse for this, what number would it be

 

You have a 2003 Ranger...............always good to include that when posting a question

Fuse 11(7.5amp) in the cab fuse box supplies 12v to battery light circuit and green wire at alternator

Test if fuse 11 slot has 12v with key on, it should it powers other systems as well, it powers Volt Meter on cluster
If so then problem will be in instrument cluster and you will need to pull it out

On the back of thecluster there are 3 connectors, 16pin, 12pin and 10pin
On the 10pin connector pins 2 and 3 are the battery light circuit
pin2 is a yellow wire, should have 12v from fuse 11 with Key on, if so wire from fuse is OK

pin3 is the light green wire that runs to alternator, use a long jumper wire from green wires end in engine bay to OHM Meter and to clusters green wire end, should have 0 ohms, direct connection, if so wire is OK, if not you will need to run a new wire(or trace old wire, up to you

If green wire tests as 0 ohms then cluster has a broken trace, usually easier to replace cluster, 1996 to 2003 Ranger clusters are direct swaps

You can get 2003 Owners manual here: https://www.ranger-forums.com/genera...1-models-3747/
To see fuse layouts and numbering
4cyl engines(2.3l) and V6s engines(3.0l/4.0l) often used different fuse layouts so "heads up", look at the correct one for your Model

 

Mazda B4000, thanks for the help. So I do have 12v on fuse 11 both sides with key on. So I did a work around and just rain 12v to the green wire, to verify the alternator is good. Alternator works just fine 13.7v, while running. Now I just have to dig into the cluster, thanks again.

 

Make sure that 12v on the green wire shuts off with the key, or you will have a dead battery tomorrow


And alternator can't just "make voltage"
If you were to just spin an alternator nothing would come out, no voltage(which is what you experienced, with 0 volt on green wire)
An alternator needs "startup voltage"..............and that's what the Green wire provides
Once alternator starts making its own voltage then green wire is now, say 13.7v, and fuse 11 is 13.7v so Battery light has BOTH terminals at 13.7v, so is goes OFF
If alternator stops making power then battery takes over, so green wire at alternator is 0 volts(ground) and fuse 11 is 12.5volts(battery volts), so battery light is ON

But here's the thing, an alternator is very similar to an electric motor, so when you give it 12volt it will try to spin, it can't of course because of fan belt, but it will still try.............
So full time 12v on green wire = Dead Battery in the morning

 

I bought the truck as is, guy said battery went dead so he bought a new one put it in. Then the alternator went out. Replaced that and now it won’t charge. Would a bad ground cause this? And do I just check the 3 battery grounds? The battery light works all fuses are good.

 

Welcome to the forum

You should start your own thread

A failing alternator kills a battery
A failing battery kills an alternator

So if not tested both often need to be replaced, and IF it was the alternator............................it can then take a NEW Battery down with it unless it was tested, bummer $$$$

Fortunately testing vehicle charging systems is easy and straight forward
Need a Volt Meter, period, test light won't work

Key OFF
Test battery volts, 12.3v to 12.8v is a good car battery

On the back area of an alternator will be a larger wire connected, sometimes 2 wires on the same terminal, its called B+ terminal, thats where alternator voltage comes out so its a direct connection to the battery positive terminal
With volt meter on Battery Negative touch other probe to B+, should see EXACTLY "battery voltage", i.e. what you saw when you tested battery directly
If not Fuse or Fusible link is Blown

Now move Battery Negative Volt meter probe to alternator's Metal case, and test B+ again, should see EXACTLY battery voltage, if so Ground is OK, if lower then check the ground cables

There will be a 3 wire connector on alternator, unplug it
Test Yellow wire, use alternators metal case as Ground, red probe on yellow wire contact, should see EXACTLY battery volts
If not Fuse or fusible link is blown

Go to cab and turn on the key
There should be NO Battery light, if there is you have a shorted green wire on the 3 connector plug
If battery light is OFF that good, go to alternator and test green wire, should see "approx. battery volts" can be .2v lower that's fine, i.e. if it was 12.6v, 12.4v is OK

Plug 3 wire connector back in to alternator
Check the White wire on that connector, should be plugged into a single spade terminal on the back of alternator, check it

Start engine
Test battery volts again
13.5v to 14.8v is what you should see
Under 13.5v and alternator is bad, new or not

It really is that simple, test 3 wires
B+, battery volts key off
Yellow, battery volts key off
Green, battery volts key on


Extra credit, the green wire acts as a Ground for the battery light bulb in the dash when alternator is not spinning or not generating voltage, its also required for "startup" voltage that all alternators need to "start" generating voltage

 

The alternator good still be good if engine running and not showing charging. The belt could be stretch out or tensioner not appling proper tension causing the belt to slip on alternator not spinning it to properly charge. This was the issue on my 2001 Ranger....FYI.

 

What should the test be for checking the small white jumper wire?

 

No test for that one, just make sure its plugged in correctly on its single spade terminal