Flickering charging light

I wasnt sure if i should post this here or somewhere in electrical..

Recently my charge indicator light has been on sometimes, off sometimes, and flickering at other times. Its been changing more frequently when i go to high RPM (3500+)

So i figure it was probably a loose wire. i made sure all the battery wires were secure.

I traced the wires to the block, and noticed the fat ground wire running from the battery to the engine block was 'backed' out of its connector. But the wire itself didnt seem loose to where it would lose connection. It appears slightly corroded. Could this be it?

Not likely that wire causing the issue. How old is the battery and how cold is it where you are?

Mine has been doing this for a while now but recently it started going out just after the idle drops on warm up.

This can be caused by the voltage difference between the battery and what the alternator is supposed to be providing to keep the charge. The light comes on when there is a difference between these two voltages...

So...if your battery is older and/or is losing charge due to the colder weather it could be why it is coming on...

There should be a green/white stripe wire running from the alternator to the light on the dash...that is the one that simply turns on the light if there is a voltage drop on either side...I thought it was the cause on mine so I spent way too much time chasing that down...

Might be caused by other things...like the battery is on the way out...if it is older than 6 years and doesn't keep a charge it might be time to replace it.

I havent had starting issues.. yet. its actually been pretty warm recently. Lows in the 40s highs in the 60s. I believe the battery was made in 2011. Ill check the green and white wire. I remember seeing it.

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I would check your connection on the single wire that goes to the alternator. That is was connects to the battery light. Make sure the wire is not loose and see if there is any corrosion inside.

If that connection is good. The next thing I would check is simply the bulb in the dash. Might be loose or going bad. If you go that far might as well just replace all the bulbs in the cluster since you have it out. I need to pull my cluster to get to a relay so I already ordered new bulbs on E-Bay.

Check the voltage across the battery with the engine off. Should be around 12.5 volts. Much less and you will be needing a battery soon. Now check it with engine running. Should be about 13.5 volts at idle. More right after starting and maybe a little less after running for a while.

The way the alt light works is, with the key in run and with the engine off 12 volts goes from the battery through the light and to the alternator where it is grounded. So it is shining bright.

After start, the alternator turns on/starts and puts 12 plus volts on the wire to the alt light that was grounded and so the light goes out.

Usually, when you get a flickering light or a dim light some of the diodes have failed (so you are not getting full power) or voltage regulator in the alternator is bad. But, bad wiring can happen.

Here is how the battery light circuit works.

A light bulb works when it has different voltages on it's 2 terminals.
So if you hook up both terminals to 12volts what would happen?
Nothing .............with 12volts on both no power is passing thru the bulbs filament so it won't glow(light up).
If you hook up one terminal to 12v and the other to 0v(ground) power would start to flow thru the filament and bulb lights up.

Battery light gets 12volts from ignition switch on one terminal when key is turned on, it's other terminal is connected to alternator's voltage regulator(in alternator).
When engine is off the alternator is not producing power so is a Ground(0 volts), battery light is on, 12volts on one terminal 0 volts on the other.

When engine is running alternator is producing power, 13.5 volts, or higher, so now battery light has 13.5v on one terminal and 13.5 volts on the other, bulb is off because no power is passing thru it, both terminals have equal voltage.

Lets say engine off battery voltage is 12.5volts
If alternator should start to fail and its voltage drops below 12.5volts then battery light will start flickering because battery's 12.5v is passing thru the bulb to failing alternators 12volts or less.
It could be voltage regulator issue or alternators fields but voltage is down below battery's voltage which means problems.

Diagram here: http://www.therangerstation.com/tech_library/EDiagrams/files/Diagram_charging_1991_2.JPG

Look at the alternator "I" wire, LG/R wire(light green/red stripe wire), this is the Battery Light wire.
This is on the 3 wire connector on the alternator.

You will also see this light bulb has a resistor by-pass, that is because this wire is also the ON/OFF switch for the alternator, it is dual purpose.
An alternator will draw power from the battery if left on all the time, the internal voltage regulator needs the battery voltage on the "I" terminal to "turn on" alternator.
The resistor is there in case bulb burns out, without the resistor the alternator would not charge battery with engine running, it would be OFF, it is a failsafe so burned out light bulb won't leave you stranded with dying battery.


First get a Volt Meter, test battery voltage with engine off
12.3-13volts
Start engine should now be above 14volts, battery is being recharge from starting drain, should stay under 14.9volts
After running for 3 to 4 minutes voltage should be 13.5-14volts, this keeps battery charged but won't "cook it"
Rev engine and hold it at approx. 2,000rpm, voltage should go up then drop down to what it was before, 13.5-14volts
That is the voltage regulator doing its job, maintaining battery voltage without overcharging it.

At idle turn on all the lights, heater fan and anything else, voltage should drop and then come back up to 13.5-14volts

RonD .... very nice explain.

I knew the basic parts of what you explained, but did not know why there was a resistor in the circuit. Now I do.
Thank you...
tom

I had this problem on my ranger. On the back of a 3G alternator, there is a single plastic connector that is separate from the voltage regulator connector. The tab broke off on mine. The wire was loose. When you wiggle it, the light flickers. I bought a new connector from Rock Auto and just replaced it.


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Check this out: http://www.therangerstation.com/forums/showpost.php?p=1509142&postcount=471


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Got 12.4 after truck had been sitting all weekend. When i cranked it the voltage was hovering between 15-16V! Once it warmed up it was bouncing between 14-15V. Stayed the same when i turned on all accesories.. And i didnt see the battery light yet this morning. about to check alternator connector if i can

EDIT: i took off the air intake tube to get a better look, and i noticed the stator wire is indeed loose. thanks much! Could this cause the overcharging problem? I dont plan on driving it with this overcharging issue.

twfmvm said:

Got 12.4 after truck had been sitting all weekend. When i cranked it the voltage was hovering between 15-16V! Once it warmed up it was bouncing between 14-15V. Stayed the same when i turned on all accesories.. And i didnt see the battery light yet this morning. about to check alternator connector if i can

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Click to expand...

That's good...sounds like the alternator is doing it's job...

did you get a chance to check the green wire? I am just curious as to what colour the stripe is on yours because so far I've found slight discrepancies in wire colours from what is shown in the manuals...could be just a Canadian thing but I can't see whey they would do that.

I think its the green and pink wire. im not certain. Its the only green wire coming out of the connector. Theyre all really dirty though

I thought 16v wasnt safe for 12v electronics?! Can i drive it without cooking anything? Isnt 16v overcharging?

Yes, 16volts is not good, 14.9v maybe 15.2v for a short time if battery was really dead, or it is very cold outside

The flickering battery light can also be from Over Voltage.

I would suspect voltage meter first but 12.4v with engine off is good reading if engine cranked and started, so meter is not reading high.

Switch your meter over to AC Volts
Start engine, put red probe on B+(big terminal on the back of the alternator)
Put black probe on a good ground
.5 VAC is the most you should see, more than that means diodes are failing.

Alternator generates AC Voltage when spinning, there are 3 sets of diodes that convert the AC to DC.
Leaking AC can cause over voltage

From time to time i notice at low rpm or idle that my trucks voltmeter needle swings up and down as if its getting AC. Id gotten so used to it i forgot to mention it.

I decided to drive it and the voltage did go down significantly after driving it. My stereo has a voltmeter display built in (it reads .5 or less low) and displayed 14v.

EDIT: wizkid do you have a link for that connector? can't seem to find it?

2nd EDIT: i checked the ac voltage from b+ on alternator to battery negative. It was between .1-.3 volts.

I tightened the two T15 torx screws holding the voltage regulator to the alternator, and it appears to have fixed the problem of oscillating voltage. Thought this might be useful

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