Battery warning light

Hello there,

I have a 1999 Mustang GT and have the battery warning light coming on and off intermittently for the past 3 months or so.

Alternator was replaced 2 years ago and battery less than 1 year ago.

Car starts up and drives just fine and never had any issues until today.

This morning when I went to put the key into the run position, I noticed that all the analog dials swept to the max position and back to zero. Car starts up just fine. I drove it about 1-2 miles and parked.

Came back to the car, key into run position and the dials swept through again. But when I tried to start, the starter clicked and loss all power to the car. No dome lights, no trunk lights, nothing. Like there wasn't a battery in the car.

Popped the hood, and disconnected the negative cable from the battery. I reconnected the negative cable to the battery and the power came back on in the car. Key back in run position, dials sweep and car starts up just fine.

Drove another 1-2 miles and parked for about an hour. Went back to car, key in run position, dials do not sweep and starts up just fine. Drove 3-4 miles and the battery warning light came on for a bit, then went away and came back on again.

From my Google search, I found a lot of people saying to "check the grounds". I really don't know what that means.

Any ideas? Help! Thanks a bunch.

You could have autozone test your battery, and you could take the alternator out and have them bench test it.

As far as grounds, its possible you have a faulty ground wire. Either loose, corroded connections or a broken wire. I believe the main ones are the engine ground thats attached to the engine block. The other is attached to the back of the intake manifold or cylinder head. Check both ends of both cables, and the entire cable. Make sure they are tight and corrosion free.

First make sure your battery terminals are clean and tight. You should not be able to twist or remove them by hand. Then have the battery and alternator tested. Many parts stores will do this for free.

If everything checks good, it can still be the battery. I have seen batteries have cell plates that separate inside and move causing the battery to test good one minute and show a bad cell the next. Unless you test it right when it's acting up they can be hard to catch.

From your description I'm doubtful there is a ground problem. It's more likely loose or dirty battery terminals or a seperated cell in the battery.

Thanks for the replies fellas.

I'll start by getting some battery contact cleaner and clean all the contacts and wires. I suspect (or hoping) that the wires are the issue since they are 18 years old. The alternator is 2 years old. The battery (brand new Motorcraft direct from Ford) and battery clamps are 1 year old with no signs of corrosion when I disconnected/reconnected them when I loss power two days ago.

Will post updates to this thread. Thanks again!

Update.

I took the battery out, cleaned the terminals with battery cleaner and a wire brush. Took the battery clamps off the wires and cleaned that. And also cleaned the wires. Put it all back together and the battery light came back on and off, and on intermittently again.

Went to O'Reilly's and the friendly and helpful counter person went out to the car with me and used their hand-held tester and tested the battery with the car off and then with the car running and their device came back with starter-ok, Alternator-ok but battery bad.

Will head to Ford parts counter on Monday and get them to swap it out under warranty and go from there.

DHG1078 said:

You could have autozone test your battery, and you could take the alternator out and have them bench test it.

As far as grounds, its possible you have a faulty ground wire. Either loose, corroded connections or a broken wire. I believe the main ones are the engine ground thats attached to the engine block. The other is attached to the back of the intake manifold or cylinder head. Check both ends of both cables, and the entire cable. Make sure they are tight and corrosion free.

Click to expand...

I re-read your instructions and looks like that is my next step: check the ground that attaches to the engine block.

Latest update.

Went to get the battery and alternator tested out of the car. Both tested twice and both passed each time. Tech recommended checking grounds. ie. follow the battery wires and making sure everything is clean and tight. He said to pay careful attention to the wires going to the engine block and starter solenoid.

So basically back to square one, but at least I can rule out the battery and alternator since they have been tested 3 times now.

Thanks again guys!

macuser27 said:

I re-read your instructions and looks like that is my next step: check the ground that attaches to the engine block.

Latest update.

Went to get the battery and alternator tested out of the car. Both tested twice and both passed each time. Tech recommended checking grounds. ie. follow the battery wires and making sure everything is clean and tight. He said to pay careful attention to the wires going to the engine block and starter solenoid.

So basically back to square one, but at least I can rule out the battery and alternator since they have been tested 3 times now.

Thanks again guys!

Click to expand...

I've returned batteries where the insides were damaged and the batteries were "hissing" and bubbling but passed when tested at walmart. Don't rule out a bad battery, but check the other stuff.

Can pretty much guarantee it's your alternator is going out. Buy a cheap volt meter from auto parts store and put it to the battery with the Engine running, if you are not getting around 13.5-13.8ish volts then your alternator is not fully charging.

I don't know what the threshold is for a fail according to the test equipment, but since the light is going on and off, you have an intermittent issue. Best thing to do would be to check voltage output with a voltmeter at the battery whenever your battery light is on while the Engine is running.

I figure that O'Reilly's would be inclined to have my battery and/or alternator fail to they can sell me replacements. But alas, that is not the case.

So I went home and checked as much wiring as I can in the engine bay and it mostly looks good.

Then I went under the car and checked the ground wire that connects the engine block to the frame and it was extremely rusty on the frame end. I disconnected that wire from the frame and started the car and it did not trigger the battery light. Weird.

macuser27 said:

I figure that O'Reilly's would be inclined to have my battery and/or alternator fail to they can sell me replacements. But alas, that is not the case.

So I went home and checked as much wiring as I can in the engine bay and it mostly looks good.

Then I went under the car and checked the ground wire that connects the engine block to the frame and it was extremely rusty on the frame end. I disconnected that wire from the frame and started the car and it did not trigger the battery light. Weird.

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It could be a pending CEL. The light doesn't always come on immediately. Sometimes the problem has to occur on enough cycles to light the CEL.

Sounds like you might have a pretty easy fix.

macuser27 said:

I figure that O'Reilly's would be inclined to have my battery and/or alternator fail to they can sell me replacements. But alas, that is not the case..

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I'm telling you, just get yourself a $7 voltmeter, stick it to the battery with the engine running and see for yourself what kind of voltage your alternator is actually putting out. Probably in your best interest to replace that ground while you have it loose. Check the nut on the alternator power cable, alt was replaced, who knows, maybe they didn't fully tighten it and you've got a poor connection.

StrayBullitt said:

I'm telling you, just get yourself a $7 voltmeter, stick it to the battery with the engine running and see for yourself what kind of voltage your alternator is actually putting out. Probably in your best interest to replace that ground while you have it loose. Check the nut on the alternator power cable, alt was replaced, who knows, maybe they didn't fully tighten it and you've got a poor connection.

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The engine block ground is the main ground for the starter and alternator, IIRC. That could be the loose connection.

DHG1078 said:

The engine block ground is the main ground for the starter and alternator, IIRC. That could be the loose connection.

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If I understand correctly, he's saying he took that ground loose on purpose and ran the Engine and it did not turn on the battery light.

The only way to take the alternator out of the loop I believe is the terminal on top.

Just buy a new alternator and you will be fine the battery light indicates that your alternator is bad been through three of them myself.

StrayBullitt said:

If I understand correctly, he's saying he took that ground loose on purpose and ran the Engine and it did not turn on the battery light.

The only way to take the alternator out of the loop I believe is the terminal on top.

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If the ground is not secure, they battery isn't charging. You need the ground to complete the circuit.

StrayBullitt said:

If I understand correctly, he's saying he took that ground loose on purpose and ran the Engine and it did not turn on the battery light.

The only way to take the alternator out of the loop I believe is the terminal on top.

Click to expand...

Maybe I'm not remembering the wiring correctly. IIRC, the battery is grounded to the chassis directly, then the alternator is grounded to the block, and the block is grounded to the chassis. If the engine to chassis ground is bad, there isn't a good return path for the alternator which could effect charging.

I think its the same for the starter. Ground goes to the engine and then the chassis, and if there isn't a good connection to the chassis, it won't work as there isn't a good return to the battery.

StrayBullitt said:

I'm telling you, just get yourself a $7 voltmeter, stick it to the battery with the engine running and see for yourself what kind of voltage your alternator is actually putting out. Probably in your best interest to replace that ground while you have it loose. Check the nut on the alternator power cable, alt was replaced, who knows, maybe they didn't fully tighten it and you've got a poor connection.

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I didn't realize one could be gotten for that cheap. I'll look into that. Thanks. The nut is on the alt is definitely clean and tight.

StrayBullitt said:

If I understand correctly, he's saying he took that ground loose on purpose and ran the Engine and it did not turn on the battery light.

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Correct. I left that ground disconnected on purpose and found it weird that the car started up and stayed running and not trigger the battery light.

maxwell6 said:

Just buy a new alternator and you will be fine the battery light indicates that your alternator is bad been through three of them myself.

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That will be the last resort. Still looking for "free" fixes as I have a Lifetime Warranty on the current alternator.

Thanks for all the replies. My next step is to get Ford to swap out the battery since it is also under warranty.