Battery Indicator Light Comes On For 2-3 Sec Than Go's Off

TmanGT

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Feb 1, 2015
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It's a 2001 mustang gt. It doesn't happen often about 2 weeks ago the battery indicator light came on. It did it again today and it was after I had the battery/alternator tested only to find out they where fine. So I don't understand why that light flashes on. Any ideas? I owned this car for about 2 months now just fixing up minor issues.
 
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wmburns

SN Certified Technician
Aug 14, 2009
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The dash battery light comes on anytime the voltage drops below a certain level. Some things that could cause this are:
  • Bad alternator
  • Bad battery. note, a bad battery CAN cause the alternator to stop putting out.
  • Bad/loose battery cables
  • Bad/loose/dirty grounds
  • A large "step load" increase in electrical demand.
  • Motor RPM's too low
It would help trouble shooting to have a better idea of what else is going on at the same time. For example, did the AC just turn on? Or how about the RPM's fell and then recovered? Turned on some electrical load say a fan or urber radio system?
 

TmanGT

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When it came on the couple times I seen it. I was running the ac the first time at a dead stop at the red light, the second time I was running the heater moving in first or second gear.
 

squeak93

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Jun 2, 2005
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Check for corrosion at all terminals, especially the grounds. I wouldn't just start throwing money at it in hopes to fix the problems. Unless the cable has visible damage or has been pinches/cut etc then there likely is just a cable end problem that is cheaper and easier to replace just the ends (sanding works well too).
 

TmanGT

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Feb 1, 2015
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Come on again today for about a min this time. Do you think it may be a pulley issue? I see my rpm drop by 200 then go back up again for reason I feel that it is. Opinions please.


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wmburns

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Do you have UD pulleys? Do you suspect belt slip (note if true there would be other evidence present such as noise)? What have you done to rule out the other likely possible causes previously suggested?

What about the AC system? Is it low on Freon?

The problem here is you don't know if the RPM drop is causing the battery light to come on or a problem with the alternator is causing the RPM drop.

Bottom line. Today's cars simply will not run right without a strong battery and charging system. That's why virtually all electrical problems should start with a through review of the battery and charging system. Only then move on to other testing. This is how I would go about fixing my own car.

THEN I would move on to the being a possible low idle issue. IE, the motor's RPM's drop which causes the battery light to come on.

Here's some information on how to trouble shoot Idle/IAC issues:

Troubleshoot IAC idle problems 1996-2004 | Mustang Forums at StangNet
 

squeak93

10 Year Member
Jun 2, 2005
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You can also run to just about any parts store and they can test the battery and charging system. It will at least help eliminate some issues. As WMburns stated, under drive pulleys can also cause issues.
 

TmanGT

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You can also run to just about any parts store and they can test the battery and charging system. It will at least help eliminate some issues. As WMburns stated, under drive pulleys can also cause issues.
Had that done everything checks out ok
You can also run to just about any parts store and they can test the battery and charging system. It will at least help eliminate some issues. As WMburns stated, under drive pulleys can also cause issues.
 

Mineral4.6

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Mar 17, 2015
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my battery light would flicker under really hard acceleration a few times before. Turned out my issue was the harness plug that hooks to alt. was vibrating out of position due to the plastic clip that holds it tight was broken. $20 at autozone.
 

TmanGT

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Feb 1, 2015
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Ok so back again. This time something actually happened this time I completely drained my battery I stopped to the nearest auto parts store had my battery recharged and tested. Once again battery tested fine so I decided to buy a alternator which turned out being the wrong one after I pulled the old one. So I went back to the auto part store to get the right alternator I decided to bring the old one to get tested. It passed so I just got my money back. Once again now I'm confused and don't know which to buy or if I need to buy at all. Cables or fine belt is fine. Also I found out that the alternator I have is a 105 amp is that stock with all 2001 GT'S? Previous owner replaced it so maybe not enough amps? I need help I'm already sick of this issue I want it resolved asap so I can move on with my life please help
 

wmburns

SN Certified Technician
Aug 14, 2009
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Also I found out that the alternator I have is a 105 amp is that stock with all 2001 GT'S? Previous owner replaced it so maybe not enough amps?
Do you have an Uber sound system? Or some other HUGE power drawing device? Unless you do, the 105 amp alternator is NOT your problem. Think how many Mustangs were built, lived, and died all left the factory with a 105 amp alternator. Most had no issues with flashing dash lights or the battery not charging.

I can almost promise you there's a reason for your problems. However, since you are certain that the "usual" causes check out fine, this means the problem is likely more esoteric.

Do you have a volt-Ohm meter (VOM) are are you willing to use it? If so one of the tests is to confirm the ground between the alternator case and the battery negative. Need two readings. With the motor running, measure the voltage between the alternator case and the battery negative. Post.

Now measure the voltage at the battery. Post. Even better is to repeat the measurement when the dash battery warning light is on.

Next with the motor off measure the Ohms between the alternator case and battery negative. Should be low. Be sure to zero the VOM meter before taking the measurement and use fresh batteries in the VOM.

Another possibility is a bad ground behind the center console. This ground is shared by multiple devices including the cluster and radio. This ground is frequently messed up during a radio install.

Yet another possibility is a cluster problem. IE, the dash warning light is false. For this we really need to know the voltage at the battery.
 

TmanGT

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Feb 1, 2015
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Just purchased a brand new battery this morning exactly what I did want is to have the same problem that's exactly what happened so if get a new alternator will it fix the issue hard to tell.
 

TmanGT

Member
Feb 1, 2015
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38
Do you have an Uber sound system? Or some other HUGE power drawing device? Unless you do, the 105 amp alternator is NOT your problem. Think how many Mustangs were built, lived, and died all left the factory with a 105 amp alternator. Most had no issues with flashing dash lights or the battery not charging.

I can almost promise you there's a reason for your problems. However, since you are certain that the "usual" causes check out fine, this means the problem is likely more esoteric.

Do you have a volt-Ohm meter (VOM) are are you willing to use it? If so one of the tests is to confirm the ground between the alternator case and the battery negative. Need two readings. With the motor running, measure the voltage between the alternator case and the battery negative. Post.

Now measure the voltage at the battery. Post. Even better is to repeat the measurement when the dash battery warning light is on.

Next with the motor off measure the Ohms between the alternator case and battery negative. Should be low. Be sure to zero the VOM meter before taking the measurement and use fresh batteries in the VOM.

Another possibility is a bad ground behind the center console. This ground is shared by multiple devices including the cluster and radio. This ground is frequently messed up during a radio install.

Yet another possibility is a cluster problem. IE, the dash warning light is false. For this we really need to know the voltage at the battery.
I'll get back with you tonight with that meter test also I'll check behind the radio check the ground
 

TmanGT

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Feb 1, 2015
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Update issue addressed went to pep boys one time they said it was a bad alternator/ bad diode major voltage drop. Keep in mind I went to advance auto parts for free battery/ alternator check 5 times and their machine said everything was good. I paid 16.99 for pep boys to run check and right there I knew what I need to replace "thank you pep boys" besides them wanting a $105 for labor to install it lol..... I said no I can manage it went to advance auto parts to get parts though the speed perks program is amazing and their online discounts. I got a 135 amp alternator for $140 brand new not a re manufacturing and the next day I got a $20 off speed perk they come quick. I test drove for 45min no indicator light. "Moving on with my life" next project!
 
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