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Discussion Starter · #1 ·
so... after some research I have replaced the alternator on my V6 mustang. Everything seemed to work just fine the first 5 minutes. After, however, the battery light on the dash board came on. After driving the car like 30 or so miles last night, I was on the highway and it decided to die. My headlights and dash dimmed, radio went out, and then the car died. After I stopped, my lights went back on temperarilly. However, when I tried starting it, it had all the symptoms of a dead battery. I checked all the wires I could get to, bolts holding them on, connectors, everything... could not think of anything that could be wrong. I got it jumped, and it ran just fine, got home and to work just now. No issues, except the battery light keeps coming on and off...


edit: maybe shoulda mentioned - the previous owner had the sterio and some other junk (cant figure out what it is yet) tapped directly into the battery. I pulled all that stuff off too. Maybe has something to do with the car running now...
 

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This should have been in the electrical forum. It sounds like you have a loose or corroded connection somewhere. Your going to have to check over the whole system with a fine tooth comb likely to find it.
 

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Check the voltage across the battery with the car idling. Make sure it reads at least in the high 13's, and not dropping.

I once fried a brand new alternator in a single day by grounding the battery lead from it to my valve cover with a wrench while trying to install it. The alternator worked and charged, but it would charge at 18+ volts. I fried the regulator.
 

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Discussion Starter · #6 ·
there were several issues.
1) my cam sensor was acting up
2) lights would dim and sometimes even go out
3) I'd lose all power and coast for a few seconds and then the car would run fine (it would not actually die tho)
4) My battery would die every other time Id start the car.

I replaced the battery and alternator at the same time.

solved the cam sensor and lights issue for a lil while, then it came back.
 

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Good point T-Bucket. 3 times I've had alternators rebuilt and although they did charge, the light was always on.

454headache makes a good test....around 14 vdc at idle, and 12 vdc with engine off.
 

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I would throw a meter on it to see what is going on. Sounds like the replacement alternator is no good or you have a bad connection somewhere
 

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I would have it tested on the car somewhere. Any repair shop should be able to test it for you and it should not be expensive. And it will certainly be less expensive than replacing parts you dont need
 

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KoTT said:
so... after some research I have replaced the alternator on my V6 mustang. Everything seemed to work just fine the first 5 minutes. After, however, the battery light on the dash board came on. After driving the car like 30 or so miles last night, I was on the highway and it decided to die. My headlights and dash dimmed, radio went out, and then the car died. After I stopped, my lights went back on temperarilly. However, when I tried starting it, it had all the symptoms of a dead battery. I checked all the wires I could get to, bolts holding them on, connectors, everything... could not think of anything that could be wrong. I got it jumped, and it ran just fine, got home and to work just now. No issues, except the battery light keeps coming on and off...


edit: maybe shoulda mentioned - the previous owner had the sterio and some other junk (cant figure out what it is yet) tapped directly into the battery. I pulled all that stuff off too. Maybe has something to do with the car running now...
Going thru the Mexican and Chinese made junk on the market I'm not surprised. Since my OEM alternator died at 160,000 miles several years ago, it's been a yearly replacement of new Autolite alternators ever since.

Put a volt meter on the dash somewhere, simply wired to a switched 12 volts an one end and grounded on the other it will tell you if the alternator is on line as anything over 12.5 to 12.7 volts is showing the alternator is supplying sufficient juice to recharge the battery and run what ever electrical equipment is operating. The typical range should lay from 13 to 14.5 volts.

Battery's need to be in good condition, internal faults can soak up a lot of power from the alternator and still not hold a charge. It takes knowledgeable person to test these things, which is done by placing a measured high power drain on the battery for a specified time to see how fast and how low its voltage will go, then seeing how quickly it'll recover. An alternator will rise to the occasion of trying to charge an internally shorted battery right up to smoking the regulator.

Never try to check the alternator's charge by running it with the battery disconnected. This can introduce some wild voltage fluctuations that will smoke sensitive electronics which these newer vehicles are full off. The battery acts very much like a reservoir where high flows can be introduced on the upstream end but a smaller constant flow is maintained on the outlet end.

Checking for whether the alternator or its regulator is a fault when the charge level is insufficient is more difficult with these one wire installations, but the trick is to momentarily short the field to ground. If the voltage swings up from nominal battery voltage (or less) to 15 or more volts then the regulator out to lunch, if nothing happens to the voltage then the alternator's windings, or its diodes, or the brushes are gone.

Bogie
 

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Discussion Starter · #13 ·
well, I just got it tested. it does not charge. and my old one did, even if the voltage jumped up and down, at least it worked... Napa bastards better refund me my money for sellin a sucky alternator.
 

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Discussion Starter · #14 ·
hypothetically speakin, what happens if you ground the wrench you use to attach the cable on the alternator to something? what would go out? the alternator it self, some sorta fuse, or what?
 

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It's not Napa, it's who does their rebuilding. Oh what do I know, maybe there's Napa Alternator re-building factory.

Anyway, as many have said, it's not a surprise. I once bought a rebuilt Ford Starter. Somtimes it would spin and not crnak engine. So I took it apart. The ground for the throw-out coil was riveted to the starter frame, BUT, the frame had been painted first. So depending on the weather (outside air temp) sometmes it would work, and sometimes not. I fixed it by tapping the rivet hole and installing a machine screw.

However, to be fair, could it be that something in your car loaded the alternator to the point it burnt out? A bad battery can do that, but I take it you replaced both at the same time. Any intermittent wiring that could cause a "short" could also do it.

Good luck on getting your money back. I really hope you do, but I don't think they like accepting returns on electrical parts.
 

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Discussion Starter · #16 ·
yes, I did both at the same time... neways. they have a 3-year warranty... or at least so the receipt says. bastards :smash:

but, that's a good point tho. I ma put my old one on first, and see what happens.
 

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KoTT said:
hypothetically speakin, what happens if you ground the wrench you use to attach the cable on the alternator to something? what would go out? the alternator it self, some sorta fuse, or what?

Shorting the output of the alternator to ground will toast the diodes in short order. If this is what you did they may not take it back.
 

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KoTT said:
hypothetically speakin, what happens if you ground the wrench you use to attach the cable on the alternator to something? what would go out? the alternator it self, some sorta fuse, or what?
If the alternator was running it would see this as an increased demand for output, it would rise to the occasion and if the load lasted long enough the diodes or regulator would probably give out first.

If the alternator was not operating, such a short would actually be between the battery and ground, aside from putting on a good spark show, nothing should happen to the alternator since it wouldn't be directly in that circuit. But electronics being the sensitive things they can be, and diodes do leak a little backward current, so there is a little connection to the battery circuit even when the alternator isn't spinning. So such a short might take out the diode pack of the rectifier. I really wouldn't expect it to do that, but if I saw it smoke the diodes I'd have to just shrug my shoulders and go "sheet happens".

The output circuit of the alternator to the battery is usually not fuse protected. Sooo this can get ugly if there's a dead short for more than a moment.

My old 78 Scottsdale short bed peekup shorted the starter cable to the headers one day while setting in a parking lot, this being the same circuit just a bit further away from the alternator. Saw a lot of smoke coming out from under the hood while renewing my DL, the lady behind the counter called the fire dept., who drove on past and never did show up while I was the there. Eventually the smoke cleared, I walked over raised the hood saw all the melted insulation, pulled the now naked wire off the header, yeah it was hot. Walked over to the parts store on the other side of the strip mall, bought a new cable and a wrench. Took off the toasted cable, put on the new cable. Got in twisted the key and the 454 fired right up, no problems, aside from my surprise. Went home, never did see the fire department, never had a following problem from the incident. I did reroute the starter cable and tie it down. Loaded the back with camping gear and left Seattle for Yellowstone the next morning. Costco premium battery, how about that.

Bogie
 

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Discussion Starter · #20 ·
cool. so it musta been fried to begin with :)

my main concern tho - could a human body be the ground (assuming Im touching the fender while I work?) cause if it could, there is a slim chance I mighta messed up big time... heheh...
 
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