only charging 12v alt checked good

Trevorbarnes · Oct 26, 2013

1999 ranger 3.0 4x4. its only charging 12v when running and replaced the alt and got the new one checked again thinking it might be bad but it checked good. i ran new grounds and positives outta 4 gauage wire and left the factory wires to and nothing. no fuses are blown either?

RonD · Oct 26, 2013

Reads like alternator is not turning on.
Alternators have a on and off "switch", otherwise they would drain the battery when engine was off.

There is a circuit that is powered(12v) when key is turned on, it runs thru the battery light and or Volt meter on dash and then to the alternator, usually light green wire on the alternator, this 12v turns on the alternator when key is on.

There is also a short jumper wire(white) on the back of the alternator, this wire can get frayed and is only partially connected, any of the 3 smaller wires can get frayed, so check them all.

Use a volt meter and check for 12v at that connector with key on(12v) then key off(0v)

There are "one wire" alternators, these use RPM to turn on and off the alternator, these avoid having to have to 12v on/off "switch".

Trevorbarnes · Oct 26, 2013

okay so i went and checked the connections. there is only one wire that gets power when the key is turned on and its a bigger yellow one(12v).

RonD · Oct 26, 2013

That's probably the Load wire, forgot about that one, it monitors voltage for the regulator.

Does the battery light on the dash come on with the key on, and then stay on after engine starts?

No light with key on means no power is passing to turn on the alternator, that could be a problem in the ignition switch or a fuse, inside the cab.

Older diagram here, colors may not match but "I" is the connection at the alternator that needs 12v for alternator to start putting out power on B+(the big wire)
http://www.therangerstation.com/tech_library/EDiagrams/files/Diagram_charging_1991_2.JPG

Trevorbarnes · Oct 26, 2013

i dont think the battery light is even coming on at all

RonD · Oct 26, 2013

Trevorbarnes said:
i dont think the battery light is even coming on at all

Then that would be where the problem is, not the light bulb, even if it was burned out(not likely) there is a 500ohm resistor by-pass so power will still go to alternator.

It shows Fuse 15 being the power for that circuit

Google: autozone 1999 Ranger wiring diagram

Repair guide Ford Ranger/Explorer/Mountaineer 1991-1999 is what you want

Figure 37, lower right, shows charging system for 1999 ranger 3.0l

Trevorbarnes · Oct 26, 2013

fuse 15(7.5a) is good in the fuse panel of the truck. where would the 12 ga fuse link be located? what about the other nca (15a)?

RonD · Oct 26, 2013

Measure the Voltage at the Big wire on the alternator with engine running, if it is the same as battery voltage, 12.5v(approx) then fusible link is good, if it's 14volts then fusible link is bad.
Follow that big wire and you will see a black(usually) square that it connects to, that's the fusible link, usually near the battery, the fusible link is also connected to the "+" battery terminal.
A fusible link is a "slow-blow" fuse, so very short voltage spikes won't burn it out.

The other fuse will be in the power box under the hood.

A working alternator will show 13.5volts minimum, when spinning at idle, on that big wire terminal on it's back side, but only if it is turned on by the key switch, that big wire is hooked up directly to the battery "+"(via the fusible link)

What color are the wires on the 3 wire connector on the alternator?

Road Angels · Oct 27, 2013

who checked the unit, autozone , some of there personal are not to bright and think 12volts and your good to go, I went thru 2 of there units on my Marquis, one didnt work the second one the bearings howled after about 30 minutes of run time, #3 was a winner thank you ford for putingt it on top and can be zipped of quick

Trevorbarnes · Oct 27, 2013

i took the dash apart to get to the power source of the battery light, power wasnt traveling through the light ive replaced fuses and still nothing. so i simply went to the three pin plug on the alternator and stripped the green and red wire( on and off switch power source) and wired it straight to the battery it immediately started charging

im not sure where to look for the fuse or electrical problem so i might just wire it to the battery and run a inline fuse.

RonD · Oct 27, 2013

Trevorbarnes said:
i took the dash apart to get to the power source of the battery light, power wasnt traveling through the light ive replaced fuses and still nothing. so i simply went to the three pin plug on the alternator and stripped the green and red wire( on and off switch power source) and wired it straight to the battery it immediately started charging

im not sure where to look for the fuse or electrical problem so i might just wire it to the battery and run a inline fuse.

Your battery will go dead, when engine is off.

An alternator is an electric motor used in reverse, so if you apply power to it(turn it on 24/7), it will want to spin like an electric motor when engine is off, but if you spin it, engine running, it will make power, it is an AC motor so won't draw alot of DC power all at once but battery will go dead.

This is why there is an on/off switch, via the battery light circuit.

I would try to find the wiring issue at the battery light end of things.

Fuse won't help, a key on 12v, key off 0v, wire would be what to use...with the fuse.
But test voltage at battery after a few minutes of idling to make sure it drops down to 13.5volts.
Sending battery 14+volts all the time will kill it.
So there could be other issues beside the on/off

General rule is alternator should provide 1 volt above battery voltage to maintain charge in battery.
so if battery with engine off is 12.5v then with engine at idle it should be 13.5v.
After starting battery needs to be recharged so alternator/voltage regulator will send 14+ volts for a few minutes to recharge it, then drop down to 13.5v to maintain charge.

Also with engine at idle turn on all the lights, fan blower, and anything else electric, voltage should drop below 13.5v then come back up to 13.5v, that's the voltage regulator working as it should.

Trevorbarnes · Oct 27, 2013

yeah i was gonna use a key on 12v and key off 0v with a inline fuse.

i think if i do it that way though it will only charge like 14.1 consistently.

ive already checked all fuse and im not sure where else to check to fix this

RonD · Oct 27, 2013

According to the wiring diagram at Autozone repair guides:

The ignition switch should have a Green/purple wire coming out and running to the inside fuse panel, fuse 15/7.5amp, have you checked that there is 12v there with key on?
If not then ignition switch may have a bad contact.
Ignition switch isn't the Lock cylinder the key goes in, it is under the steering column, the key just slides a rod to move the ignition switch to make or break several contacts.
Video on where and how to replace that switch if needed: http://www.youtube.com/watch?v=j3I2oye8OpQ

If you have 12v at the 7.5 amp fuse then a yellow wire should leave that fuse and go to the Battery light.
Then the light Green/red wire from light to Alternator.

Trevorbarnes · Oct 28, 2013

Replaced all fuses yet again and went thru a lot of wiring and got the truck charging without straight wiring it

RonD · Oct 28, 2013

Hey, good work :icon_thumby:

So no specific, "that's whats wrong" wire?

only charging 12v alt checked good

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