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Discussion Starter #1
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.
 

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Start by testing the battery just to make sure you didn't get a lemon. Also, check all the cables that go from the battery to the starter, as well as, the alternator power cables. You want to make sure all connections are clean and tight.
 

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That sounds exactly like a negative/ground connection issue. The dead give away is the dash instruments go from max to zero. They do that when they loose connection to the battery. I am experiencing the same type of thing, though slightly different experiences, and for me I know the negative terminal that connects to the battery is bad and I just need to replace it. Even though the negative terminal is "on" the negative stud of the battery it still looses the connection because the terminal isn't tight enough on the negative stud even though the nut it as tight as it will go.

Make sure there is no play on the negative terminal and stud. Follow the negative cable and verify that it is properly connected to the body and engine.
 

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Discussion Starter #4
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.

Will post updates to this thread.
 

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Discussion Starter #5
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.
 

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It's awesome that you came back to fill everyone in on what it was. Hopefully it is just the battery being sold to you as a lemon and you are able to get it replaced for free under warranty. Free fixes are the best!
 

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Discussion Starter #7
It's awesome that you came back to fill everyone in on what it was. Hopefully it is just the battery being sold to you as a lemon and you are able to get it replaced for free under warranty. Free fixes are the best!
It's good to update threads so when someone else stumbles upon this, they would have an idea of what direction to go. I just read back your previous reply and looks like that is my next step: Follow the cable from the battery to the starter/starter solenoid. I only cleaned the ends attached to the battery terminal. The power wire to the alt is also clean and tight.

That sounds exactly like a negative/ground connection issue. The dead give away is the dash instruments go from max to zero. They do that when they loose connection to the battery. I am experiencing the same type of thing, though slightly different experiences, and for me I know the negative terminal that connects to the battery is bad and I just need to replace it. Even though the negative terminal is "on" the negative stud of the battery it still looses the connection because the terminal isn't tight enough on the negative stud even though the nut it as tight as it will go.

Make sure there is no play on the negative terminal and stud. Follow the negative cable and verify that it is properly connected to the body and engine.
Cool. I cleaned and tightened the ends on the battery terminals so next step is your instruction to follow the negative cable to the body and engine. My instrumentation never goes down like yours - always stays in the good range. It's just the battery light coming on intermittently.

Thanks again to the BOTH of you.

Anyway, was going to post this 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.
 

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Discussion Starter #9
Ground going to the block is the most common issue.
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 that 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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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 that 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.
Probably because you opened the circuit by doing that. You should replace it with a new cable and make sure the connections are clean and you should be good to go.
 
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