2000 Ford Ranger 2.5L will not start

AlanD:"Why do alternators even need an OFF switch?
Because they can act as an electric motor, if you leave them connected to power, the rotor part, they will try to spin the fan belt, and of course they can't, lol, and this will drain the battery pretty fast."

Alan, how does a 'slip ring' rotor work as a motor if it is fed DC voltage? Don't DC motors need a commutator with individual bars for each of the windings on the rotor? I knew old generators could be 'motorized'(and you had to touch power to the field(?) when you installed a re-man to polarize the electromagnet- been a Looonggg time)
All I know about the warning lights fits what you said, except I hadn't heard about the warning light providing the exciting current for the field(right?). I thought the light was in parallel with a 'shunt', but never dug into the details, just accepting that...
I remember on old vehicles my dad set the idle low enough the generator light would flicker or glow dimly(or brightly, depending... it's been a long time) as it was provided a potential difference(voltage) across the 'ground' case and the 'B+' pointy end. If the generator was cooking properly, it was V vs V butting heads, mental image, and the light did not light. I sort of remember if you had some bad windings in the rotor, you may get a dim glow even with the engine running at highway speed. Boy, that was a while ago.
tom

Ok it has been about 2+ months since I posted. Everything is running. It seemed like every time I posted that all was well something else happened. That being said I have the battery light on but the volt meter is reading correct or at least it is in the same position. why is the batt light on with no apparent problem.

Battery light circuit serves 2 purposes
When you turn the key on the Battery Light gets 12volts from a fuse in cab fuse box, in 2000 Ranger its Fuse #15, 7.5amp
This 12v travels thru the bulb to the Voltage regulator(the Green wire on the 3 wire connector)
This 12v is used by the Voltage regulator as Start Up voltage
An alternator can't just generate voltage by spinning it.
It must have Start Up voltage for the rotor, so when rotor starts to spin it can start to generate its own voltage.
If this Start Up voltage was left on all the time then it would drain the battery.
So it's Key on voltage

A light bulb only lights up when there is voltage moving thru it to heat it up
With key on engine off the alternator/voltage regulator is low voltage, like a ground, so voltage flows thru Battery Light Bulb to alternator causing the Battery Light to light up.

When engine starts, alternator starts to make voltage, say 14volts.
So the voltage regulator now has 14volts, and the FUSE in the cab for Battery Light ALSO has 14volts
If a light bulb has 14volts on each terminal then no voltage can flow, it is equal, so light is off.

If battery light is on it means battery light bulb has two different voltages, engine running or not.
That's just what it means

It could mean the Green wire on alternator is shorted to Ground in the harness
It could be voltage regulators diodes are bad, so green wire is not getting the 14volts, or what ever alternator is outputting.
It could mean alternator is outputting below 12volts(battery voltage), i.e. fuse has 12v Green wire has 10volts.



You will need a Voltage meter to test the system.
key and engine off
Test battery voltage, and remember it exactly
12.3v to 12.8v is a good battery, under 12.3v is a failing battery, 5 to 6 years old usually

Test B+ terminal on the back of alternator, use alternator's case as the Ground for the meter, should show Battery Voltage

Unplug 3 wire connector on alternator(some voltage regulators only use 2 wires, thats fine, still test the same way)
Test Yellow wire, should have Battery Voltage

Test Green wire, should have no voltage
Turn key on, engine off
Test green wire again, should show Battery Voltage now, if lower then green wire is shorted out

If test is good then Battery light is on because voltage regulator is failing.

You can test this by using a sewing needle to pierce the Green wire at alternator while its plugged in, key on voltage should now be much lower with Rotor drawing power, and this is why Battery Light is on when engine is off(normal operation)
Start engine, green wire should now be 14+ volts, alternator voltage, if not then regulator is bad


You can start up the engine and test Battery Voltage again, should be above 14volts, 14.5-14.8v
REV engine, voltage should NOT go above 15volts, as that can damage battery, voltage regulator is there to prevent that
Let engine idle for about 5min then test battery voltage again, should be under 14volts and for sure not the same as it was just after startup, 13.5-13.8v

If its the same then voltage regulator is not working

Voltage regulators work by electrical back pressure, just after starting the engine the battery is drained a bit so there is less "push back" and voltage regulator sends out 14+ volts, as battery recharges it starts to push back so voltage regulator starts to reduce the output voltage.
When you turn on the head lights and/or heater fan to High there is less push back so voltage regulator increase output.

RonD - thanks for the troubleshooting instructions and I put in to a step by step process can you confirm the process is still correct? and have just one more question see the bolded underlined question below? Thanks, Dave

You will need a Voltage meter to test the system.
1. key and engine off
a. Test battery voltage, and remember it exactly 12.3v to 12.8v is a
good battery, under 12.3v is a failing battery, 5 to 6 years old usually
b. Unplug 3 wire connector on alternator(some voltage regulators only
use wires, thats fine, still test the same way)
c. Test Yellow wire, should have Battery Voltage
d. Test B+ terminal on the back of alternator, use alternator's case as
the Ground for the meter, should show Battery Voltage
e. Test Green wire, should have no voltage

2. Turn key on, engine off (Is the 3 wire connector plugged back in?)
a. Test green wire again, should show Battery Voltage now, if lower then
green wire is shorted out
b. If test is good then Battery light is on because voltage regulator is
failing.

* You can test this by using a sewing needle to pierce the Green wire at
alternator while its plugged in, key on voltage should now be much
lower with Rotor drawing power, and this is why Battery Light is on
when engine is off(normal operation)

3.Start engine,
a. green wire should now be 14+ volts (should be the same as battery
voltage when engine running), alternator voltage, if not then
regulator is bad


- You can start up the engine and test Battery Voltage again, should be
above 14volts, 14.5-14.8v
- REV engine, voltage should NOT go above 15volts, as that can damage,
voltage regulator is there to prevent that
- Let engine idle for about 5min then test battery voltage again, should be
under 14volts and for sure not the same as it was just after startup, 13.5-
13.8v

If its the same then voltage regulator is not working

Voltage regulators work by electrical back pressure, just after starting the engine the battery is drained a bit so there is less "push back" and voltage regulator sends out 14+ volts, as battery recharges it starts to push back so voltage regulator starts to reduce the output voltage.
When you turn on the head lights and/or heater fan to High there is less push back so voltage regulator increase output.

The 3 wire connector should be unplugged when testing Yellow and Green wires

Yellow wire will always have 12v, if fuse is good, key on or off
Green wire should only have 12v with key on, but needs the full 12v

If B+ terminal has 12v(key off or on)
And yellow and green wires test OK, then Vehicle wiring is OK, problem will be in the alternator/regulator

12v = Battery voltage, if battery reads 12.5v then thats what all the wires need to read, less means corroded or bad connection
And don't over look ground connections, that's why you should use alternators case as the ground when testing, corroded ground wire drops voltage same as corroded 12v wire

You can test Green wire while its plugged in, as a further test, it should have under 5v with key on engine off
After starting engine check battery voltage, if under 13v then alternator or regulator has failed
If its 14+ volts then test green wire(while its plugged in) and it should read same voltage, 14+, if not regulator has failed

You can just replace a voltage regulator in an alternator, but................
Age of alternator should be part of that decision, bearings, brushes(slip rings) and field coil issues can come with age

Key off battery voltage reading 12.2 VDC
Unplugged the 3 wire plug yellow - same voltage the same across the battery,
The battery is going on 4 years old.
reconnected everything and started and voltage across battery reads 14. 3.

Leever2000 said:

Key off battery voltage reading 12.2 VDC
Unplugged the 3 wire plug yellow - same voltage the same across the battery,
The battery is going on 4 years old.
reconnected everything and started and voltage across battery reads 14. 3.

Click to expand...

And green wire?

That's the important one if battery light is staying on

I removed the alternator and took to the parts store. Alternator checked SAT, cleaned all connecting surfaces and re-connected. All is working fine again no lights. I think when I spliced a new end with connector in (not quite the same as original connector) it did not make a very lasting and good connection. Anyways cleaned up and made sure new connection was good.

Have another question - this past weekend we had record amount of rain, and noticed a puddle on the passenger side floor. I mopped up and seems like it almost immediately puddled back up.
1) is this a normal occurrence and if so where do I go to unclog the issue?
2) because this is a different issue than my original post should I start another thread?
Thanks,
David