Ref: 99 Ford Ranger 2.5:

Battery warning light stayed lit, & the dash voltmeter was indicating only a 4-5 volt output, & did not rise when revved up.

The battery was still strong, & measured 12.43 volts- engine Off; With the engine running at idle it measured 11.83 volts, indicating it wasn't receiving a charge.

No engine compartment fuses were blown. I was unable to locate the Fuse-link?

I did Under-voltage check/s: Key Off , case to “F” terminal indicated battery voltage.

Key in “Run”, case to “F” terminal: Failed-- read well above the two volt limit for that test; the Haynes manual said to do a “I” circuit test; but I couldn't figure out which electrical plug terminals were “A” or “S”?

Appreciate any help.

Regards, Leigh

 

Engine off-key off
Test voltage on the back of the alternator, the B+ wire, the large one.
If it shows battery voltage, 12.43v, then Fuse-link/maxi-fuse is OK.
If it shows 0v then follow that wire it will go directly to that fuse, which is hook to the battery+.

Your alternator is not generating any power, the change from 12v to 11v with engine running shows that.

'99 charging system is pretty straight forward.
Alternator's B+ is hook directly to the battery, power on this wire runs the vehicle electrics and charges the battery.
The other wires on the alternator are to turn it on and off, and to run the internal voltage regulator.
The "i" wire on the alternator is the ON/OFF switch for the alternator, Fords usually have a Light Green/Red stripe wire there.
This wire comes from the Battery Light circuit.
When you turn on the key power from the battery runs thru the Battery Light bulb and to the "i" on the alternator.
If alternator is not turning(generating power) then the "i" will have 0volts(a Ground is 0 volts).
So if you have 12volts on one side of a bulb and 0 volts on the other side of the bulb what happens?
The bulb glows(lights up).
So when you first turn on the key the battery light should come on.
And if the alternator ever stops generating power(0 volts) the battery light will come on.

The "i" wire also turns on the alternator's circuit, allowing it to generate power, so 0 volts on the "i" wire means alternator can't generate power, Battery light coming on with the key means 12volts is there.
An alternator is an electric motor used in reverse, so if left on all the time it would drain the battery.

When alternator is spinning the voltage regulator sends about 7volts to the brushes, this 7 volts is changed into 14volts by the power of the engine spinning the alternator.
The voltage regulator varies the voltage to the brushes to change the battery, 14.8volts, and then to maintain the battery after charging, 13.6volts.
Basically if voltage regulator is working correctly you should see:
Above 14volts just after startup
And then 13.6volts after 5 to 10 minutes
As measured at the battery

General rule of thumb for voltage regulator is 1.1 volt above battery voltage to maintain battery
2.2 volts above battery voltage to change battery.
So if battery voltage is 12.5v then alternator would change it at 14.7v and maintain it at 13.6v


Battery with voltage at of below 12.2v are due to be changed, your 12.4v is probably about 3 years old, new batteries are 12.7 or 12.8v

 

Thanks so much, Ron, for the detailed account.

I'm pretty convinced that the alternator is defective---Going to get a new Pro-Start from Pep Boys, as they get very good user ratings.

Best regards,
Leigh

 

You are welcome.

Be sure to disconnect battery when installing or changing any parts.
This is for two reasons:
1. it will prevent a short that will damage electronics, and you
2. it will cause computer to re-boot on start up, this causes it to run self tests and look for any changes you might have made.

This doesn't apply to an alternator per say but more than a few people have swapped sensors or parts, then restarted engine only to find they still have a problem they thought a new part would fix.
So they go on and replace other parts, when they finally unhook the battery, a few hundred dollars later, the problem is solved, so they think that last part fixed it, when in fact the first part did.
The problem is the computer was still using the old data in memory to operate the engine so problem still seemed to be there until a reboot.
So always unhook the battery, for safety but also for the reboot.

 

Ron,

I had the battery disconnected when changing out the alternator; unfortunately the new alternator did not solve the problem. It's the same as before--Battery warning stays on with engine running, & dash volt meter needle rises about 1/4" & stays there.

Revving the engine up to "about" 4K or so--Battery warning light went out, but comes back on as soon as I back off, & dash volt meter did not rise at all.

All of the Haynes manual checks I did "passed"--(none indicated a failed regulator or alternator), but I hoped I'd missed something, & a new unit would solve the problem--but I was wrong.

The only thing I can think of now is a failed ECU; but I'm not sure how to check it out, or even where it's located?

Prior to replacing the alternator, I checked continuity from battery + to alternator output stud (with neg. battery cable disconnected) & it checked OK, .5 ohm R.

Leigh

 

Update:

I found the # 14, 30 Amp fuse blown. I hadn't noticed it when I first checked the fuses.

A costly mistake on my part.

Now the question is why did the fuse blow???

Leigh

 

I am not showing a 30amp fuse, I have a 15amp listed in 1999 wiring diagram, and it is listed in #12 slot, but in 1999 Power Distribution Box diagram it shows #15 as "alternator" fuse but no amp listed.
Never trust anything on the internet, lol.

But that should be the yellow/white wire on the alternator which you tested and would show 12v(battery voltage) if fuse was good.

It isn't uncommon for alternator fuses to blow, that is one reason fusible links are used instead of fuses.
A fuse heats up and blows fairly quickly, as it should.
Fusible link heats up but doesn't blow unless it is over amped for 10-20 seconds.

Alternators by their nature have varying voltages and amps so can blow a fuse if they get overly wet or ..................??

 

Thanks Ron,

I downloaded a 99 XLT Power Distribution diagram;

http://www.justanswer.com/ford/1bcd2...cyl-relay.html

That is the "exact" layout of the Junction Box on my Ranger. As you can see, the # 14, alternator system fuse calls for a 30 amp mini, & that's what was installed in that location.

Best regards,
Leigh