Battery Light On and Off!

[WhiteSnake74]

Hi,

Last Thursday the battery light came on so I went that same day to Advanced Auto Parts to have it checked. It came out that I had a bad alternator. So I took my car to my garage and left it there until Saturday when I replaced the alt and got a better and more powerful battery (Optima) just in case it was going bad too.

I took the car again to Advance to check if everything was ok. And it was.

When I started up the car on Sunday, the d@mn battery light came on again. I drove the car and it went off and never came back during the day. On monday morning it happened again. Today, the same.

When the car is not in use for many hours and I start it, the light goes on. But when using the car it goes off. :shrug:

What could it be?

 

[Top_Fuel]

Could be a parasitic draw. In other words, something in the car is draining your battery when the car isn't running.

Check this thread...
http://www.svtperformance.com/forums/showthread.php?t=240924

 

[sambandit]

Waht kinda pully combo do you have? Do you have a bigger crank pulley on there?

 

[WhiteSnake74]

Thanks TopFuel.

I will check for a draw.

I will try disconnecting the negative cable when the car is parked for more than an hour. If when I start the car again, the battery light doesn't show, then I have a draw.

 

[WhiteSnake74]

Waht kinda pully combo do you have? Do you have a bigger crank pulley on there?

I only have a 2.80 pulley with an aux. idler. Never had any problems until now.

Car has only 12K miles in two years.

 

[WhiteSnake74]

Well, the test is on!
I just got home and disconnected the negative battery cable.
Tomorrow morning I will connect it again before firing the car to see if the battery light shows up again.
If it doesn't show up, then I certainly have a draw.

 

[FireRed04Vert]

I'm wondering if you're new alternator is having problems energizing the fields on intitial start up. Interesting.

I don't think a draw is your problem. Even if you had one, if the car starts, you shouldn't have a warning light as long as the alternator is producing. The light isn't checking the state of your battery, but the output of your alternator. My initial thoughts are alternator/regulator issues. Did you put a "bargain basement" alternator on the car? Many of those come with off shore components and regulators that just aren't very good.

 

[WhiteSnake74]

I'm wondering if you're new alternator is having problems energizing the fields on intitial start up. Interesting.

I don't think a draw is your problem. Even if you had one, if the car starts, you shouldn't have a warning light as long as the alternator is producing. The light isn't checking the state of your battery, but the output of your alternator. My initial thoughts are alternator/regulator issues. Did you put a "bargain basement" alternator on the car? Many of those come with off shore components and regulators that just aren't very good.

Apparently is not a draw. This morning I reconnected the battery and when I fired up the car, the battery light went on again. :shrug: WTF??

I used the same alternator that I had before. The diodes where fried and they were replaced (all of them).

 

[FireRed04Vert]

Hmmm.....The regulator has to be "excited" to energize the fields. That opens up some other possibilities. I'm still saying it's in the alternator/regulator though. But I would hate to see you replace anything else without doing some more testing first and have you throw your money away. Diode failure is not uncommon and new diodes usually fix the alternator without other issues. I'm wondering if the regulator is bad too. Without further testing, I just don't know. Remind me...does the light come on when you start it then go out right away or do you have to rev the engine up a bit before it goes out? You might want to throw a voltmeter on there just for shits and giggles the next time you start it and watch it's behavior. It's a crude test, but might show you something. Just hook it to your battery posts and watch it. When the light is on, notice your voltage. Then watch it as the light goes out. Let us know the results. By the way, if the meter shows appx 14v and the light is on, that's another issue entirely....but can still be in the alternator.

 

[WhiteSnake74]

Hmmm.....The regulator has to be "excited" to energize the fields. That opens up some other possibilities. I'm still saying it's in the alternator/regulator though. But I would hate to see you replace anything else without doing some more testing first and have you throw your money away. Diode failure is not uncommon and new diodes usually fix the alternator without other issues. I'm wondering if the regulator is bad too. Without further testing, I just don't know. Remind me...does the light come on when you start it then go out right away or do you have to rev the engine up a bit before it goes out? You might want to throw a voltmeter on there just for shits and giggles the next time you start it and watch it's behavior. It's a crude test, but might show you something. Just hook it to your battery posts and watch it. When the light is on, notice your voltage. Then watch it as the light goes out. Let us know the results. By the way, if the meter shows appx 14v and the light is on, that's another issue entirely....but can still be in the alternator.

The light comes on when I turn the switch. When I fire the car, the light it's still on. If I rev it, the light doesn't turn off. I turns off after a while of driving the car. Maybe like 5 minutes of driving. Then it doesn't turn on again during the day. It doesn't matter if I run hard or just cruising.

Another thing, the light doesn't turn off quickly. It fades away slowly. Dimming out.

And remember, it only turns on when the car has been parked for many hours (overnight).

 

[Top_Fuel]

Do you have access to a multimeter like FireRed suggested? If not, you need to take it somewhere and have the alternator re-tested. You want to have it tested while the battery light is on. Then it should be obvious what's going on.

You mentioned you had it tested before and everything was OK...but the battery light wasn't on when you had it tested, right? :shrug:

 

[FireRed04Vert]

And I would add to that to have it tested by a fully equipped shop that can check amps AND volts. Leave the car overnight so they can have it first thing in the morning. Tell them to leave it parked overnight in the stall so they can check it at first start up. Good suggestion Top Fuel.

 

[WhiteSnake74]

Thanks for all your suggestions guys.

I don't have any tools to test amps and volts so I will take the car to a fully equipped shop on Saturday.

I will let you know the outcome.

 

[WhiteSnake74]

You mentioned you had it tested before and everything was OK...but the battery light wasn't on when you had it tested, right? :shrug:

Right, the light wasn't on when they tested the car.

 

[1TA2NV]

Ok so about 3 weeks ago my car died (03 Cobra). At first I thought it was the battery so I replaced it. So a day later it dies again. I charge the battery up and its good. So i figure its the alternator. So I go ahead and replace it and the car runs fine for about 3 weeks. I was driving home yesterday and the battery light on the dash came on. I thought maybe the battery was bad but I had autozone test it and they said it was good but had a low charge.

The question is, do yiu think this alternator is bad too? Is there a way to test it without have to pull it out? (When I did replace it 3 weeks ago I got the alternator at autozone. It fit and everything but the pulley on it was wrong (its was only a 5 rib pulley instead of the 7 or 8 on the cobra's) So i just changed the pulley out and it worked fine. So now I am starting the wonder if it was a alternator for a GT mustang and not a Cobra. Does anyone know if they have the same alternator but just diff pulleys. Ford has 2 diff. part numbers (one for gt and one for the cobra). Anyone have specs on these?

 

[Top_Fuel]

...do you think this alternator is bad too?
...Is there a way to test it without have to pull it out?

Yes, and yes. :-D

It sounds like your alternator has issues. Since you bought it from AutoZone, it's probably a "made in China" unit with low-quality internals...so I wouldn't be shocked if it had problems even though it's brand new.

The alternator can be tested in the car by any competent shop (I'm not sure I'd put AutoZone in that category :lol1: ). If you have access to a multimeter, you could do a 10 second check in your driveway and probably find out what's going on.

 

[1TA2NV]

Yeah, I wouldn't let Autozone touch my car....EVER! :nono: Heck ever when i had them test the battery I took it out and took it up there. No one is touching christine but me. Yeah, I might just return it and go to the Ford house to get one. I just called and they have one for 195.00 and thats what I paid at autozone. I should have gotten it from them t begin with but they were closed when my car broke down. Thanks for the help!

 

[1TA2NV]

Can anyone tell me if the GT alternator is the same as the cobra one? (other than the diff pulleys on them) Parts store has it listed as the same part number.

Thxs

 

[Top_Fuel]

You should talk to Steve. He can answer your question, AND he can sell you a Ford alternator at a reasonable cost...

http://www.svtperformance.com/forums/showthread.php?t=193978

 

[rd04svt]

Just an update....the problem with my electrical system was never pin-pointed but the dealership got permission to replace the GEM....problem solved.