Battery gauge sinking while idle. - Mustang Evolution

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Old 08-17-2014, 08:10 AM   #1
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Battery gauge sinking while idle.

Obvious problem was alternator/battery. Gauge would go all the way to 8 or lower. Radio would die lights dim before I would rev engine in neutral and get it back up. Switched alternator and battery with new from AM. Red top battery and 150 amp alternator. Engine starts at slightly higher than 12 but gradually goes down with accessories being used. Am I missing something?


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Old 08-17-2014, 08:43 AM   #2
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Maybe. Just maybe your cable going from alternator to battery might be bad. Alternator works. But the wire tht would charge the battery back up might be bad. That's why when your vehicle is running it's draining the battery. Try a continuity test on the wire. Happens allot on the hummers I work on.


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Old 08-17-2014, 08:44 AM   #3
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That migt be the issue. I sure turbo or stray bullitt would
Know more than me.


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Old 08-17-2014, 08:59 AM   #4
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Either you need to replace your cables or you have a bad ground, chasis, engine or battery.
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Old 08-17-2014, 09:10 AM   #5
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99 grumpy was I on the right track. I'm used to working on military. A little more simple then regular cars


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Old 08-17-2014, 09:43 AM   #6
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99 grumpy was I on the right track. I'm used to working on military. A little more simple then regular cars


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Old 08-17-2014, 10:30 AM   #7
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Quote:
Originally Posted by rollo1987 View Post
99 grumpy was I on the right track. I'm used to working on military. A little more simple then regular cars


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Yes, your thinking is inline with what should be the problem. Alot of times though if you start to experience draining even though the battery, alt and the other components that make up the charging system have been replaced of recent, could ultimately boil down to bad wiring, and most common fault is a faulty or broken ground, loose battery terminals and corrosion.

I know where you are coming from, I too am a military man, or at least was. I recently retired, but my primary MOS was 63H, secondary and most enjoying job was Airborne. So I worked not only on tracked vehicles, but also the M998 and other wheeled vehicles.
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Old 08-17-2014, 10:51 AM   #8
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This may just be normal for your car Steve. Some vehicles are equipped with an ammeter that indicates charge or discharge, current passing in or out of the battery. With all of the electrical equipment turned ON, and the engine idling, the guage needle may show a discharge condition. At fast idle or normal driving speeds the needle should stay on the charge side of the guage with the charge state of the battery determining how far over the needle will swing.
Some cars are equipped with a voltmeter that indicates battery voltage with the key on and the engine off, and alternator output when the engine is running.

If you have Under Drive Pulleys, it will cause the alternator to have a lower than normal output at idle.

Rollo's and Grumpy's advice is also correct... You have to give the wiring, cables, and connections a good looking over on cars that are this age. Particularly the ground connections.

Id tell you to go to AutoZone and have it all tested but since you're in Japan... There must be a place on base to have it checked out or somewhere.
You'll figure that part out.
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Old 08-18-2014, 07:24 AM   #9
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I have under drive pulleys but didn't change the alternator pulley based on testimonials from here. This only started about two months ago. Pulleys were changed back in February or March possibly even earlier. The gauge never even twitched before June and I have driven this car for two years. I just ordered a new power wire for the alternator. I will go get new battery terminals tomorrow and change those. There is some corrosion on the negative.

As far as getting help on the car (aside from the fellow military personnel here) the Japanese act scared when I tell them I need help with a Mustang. They just shake their heads.


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Old 08-18-2014, 08:30 AM   #10
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Well I would not go and just replace the cables, may not fix the issue at hand. If corrosion is on the negative, just inspect the cables and clean them up along with the battery terminals, unless you feel you must replace them. Also check your ground connections at the chassis and battery. Inspect your alt connection and see if they have come loose .
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