Hi folks, I'm new around here and I have a question pertaining to my '99 4cyl Ranger

I bought it recently from a guy who had it sitting under a tree for about two years. Slapped a new battery and tires on it and it seemed good to go. I noticed that the battery charge gauge on the dash was reading a bit low at speed, and dipping down to about 1/4 on idle. I have a mechanical background, but it is mostly all on my experience with old motorcycles and ****** jeeps, so i did what i know to do: clean off the terminals and cables, clean all the grounds, and check leads for shorts and whatnot. No dice. My next thought is that the voltage regulator may be out, so I replace it too (glad i did, because the brushes were nearly ground down to the spring!). No dice.

Anyone else got any cool ideas before I go and get a new alternator? I'm really trying to avoid it.

Glad to be here

 

One or more diodes are probably burnt out.
You should have about 14 volts at the battery when at 1000 rpm.
Test that first with a volt meter, don't trust the gauge.
Have a look at this video, it shows what a bad diode looks like.
You can take your alternator apart to where you can see the diode, but you don't have to fully disassemble it like the in the video.
Start watching at 24 minutes and keep going till about 26 minutes.

What does surprise me about your alternator is the condition of the slip ring, usually if the brushes are that worn, the slip ring will be shot too.

https://www.ranger-forums.com/genera...9/#post2124854

 

All alternators need an ON/OFF switch, or they would drain the battery when engine is off

That ON/OFF switch is the Battery Light, you mention the Volt Gauge but not the Battery Light, it should come on when key is turned on, and stay on, after startup, if alternator is not working
If it doesn't then Alternator can never start working, the Battery Light circuit allows alternator to turn ON

If no Battery Light then in a 1999 Ranger check Fuse #15 in cab fuse box, 7.5amp
(battery light bulb can burn out but there is a resistor in the circuit which still allows alternator to be turn on)

Another Fuse needed is in the Engine fuse box ALT SYS Fuse, 30amp

Ford alternators will have 3 wires
B+ is the larger wire usually attached to a Stud on the alternator, it will show 12volts all the time
Yellow wire is the feedback voltage, also shows 12volts all the time

Green wire is from Battery Light in dash, 0 volts key off, 12volts key on

Some alternators have a short white jumper, no test needed, but must be plugged in not broken

 

Hi and welcome, the key here is go by a DVOM to determine the voltage not the gauge on the dash.

What the other members here have posted should be very helpful, just keep in mind that gauge may or may not work properly.

Have you noticed any other symptoms other than the gauge reading or are you just going by the gauge?

 

I have a multimeter, I'll take a look at the voltage at idle and running rpm.


The only other symptom I've gotten is that my dome lights/headlights/radio dims at idle. Clearly my alienator is not putting out the same juice at idle as at running speed.


@ RonD
My battery light works just fine, and my fuses are all in good health

 

Alternators have 3 Field coils in the case, each Field has 2 diodes

The voltage regulator supplies 6 to 9 volts to the Rotor.
As the rotor spins this voltage creates a magnetic field around the rotor
This creates AC voltage in the 3 Field coils, the 2 diodes on each field coil changes the AC to DC Volts

After starting the engine the battery is drained a bit so voltage regulator sends 9volts to the rotor, so you should see 14.5 to 14.9 volts at the battery
After a few minutes voltage regulator will decrease Rotor voltage so battery doesn't get "cooked", optimal voltage is 1 volt above engine off battery voltage
So if battery is 12.5v engine off then you should see 13.5v after engine has been running for a few minutes.

As you increase RPMs voltage regulator will lower rotor voltage to keep it at 13.5v
At idle voltage regulator increases Rotor voltage to maintain the 13.5v

No car maker specs in an alternator that is too small for stock electrics
BUT(big but) thats if ALL 3 fields are working
If a field coil or a set of diodes fail, even at 9volts to rotor the alternator can't maintain the 13.5volts, so you get dimming lights at idle
Alternators can run that way for a long time, engine is usually above 1,500RPM when driving around, so lights are bright and battery stays charged

So dimming lights at idle is one of 2 things, fail field coil/diodes, or bad voltage regulator, i.e. stuck on 6 or 7 volts to rotor

 

Well, regulator should be good, so i'll stick the meter to it tomorrow and give it a check, and i guess i could always crack open the alternator and inspect the diodes.

Anyone had much experience replacing diodes? Or would I be better served to just get a new alt? I can do basic soldering reliably well but am not sure if it is even economical or worth my time.

 

If your going to do anything to the Alternator get a rebuild kit and rebuild it.

I personally have never rebuilt an alternator because I value my time much more than I do trying to save a alternator.

With this in mind you get what you pay for with new or rebuilt alternators, if you buy one locally insist that the store test it in front of you or just buy a Motorcraft.

 

Wrecking yard alternator, save your money
Thats all I ever use, as available