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Discussion Starter #1
hi im looking at getting my first mustang

it has a prob with the alt the owner says

it drains the battery and if you disconnect the batt the car dies

thanks for anyhelp
 

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Does it have aftermarket accessories on it?
Is a light staying on?

You can test curcuits and the Amperage pull using a digital multi meter.
 

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yea i have a very very high end custom audio setup in my car, and my stock alternator crapped out on me about 3 months back, i got a mid 90's cobra alternator that pushes alot more amps, seemed to help alot of problems, it was very very cheap fix, better off getting a nice new alt, i think my mechanic charged me $150 for evrything installed, which was nice becuase he had to custom make a bracket to get the 96 cobra alternator fit in my 91 fox
 

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I ended up upgrading to a 2001 V-6 Alt. I think it is a 120 Amp but not sure.
I am running 3 Amps and it is still having a hard time keeping up.
 

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yea same here, 3 alpine amps, 1 for each sub and 1 for the mids/highs, my lights still go nuts when the bass hits, i have a 5 farad cap i got to install, that will make the problem a little less but its to friggen cold up here in CT to work on my car!!! thats another thing, if your running any audio or alot of power draining things, a good strong battery (i.e. optima yellowtop) and a higher output alternator, (i.e. more than ur stock 85amp alt) will eliminate alot of power problems
 

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You can use a 94-95 Mustang GT 120amp alt. I have done the upgrade myselft and it was simple. You will need to grind some of the bracket away, but that is the hardest part if you can do the wiring. There are instructions (3G Upgrade) on here or on many other sites dedicated to Mustangs.

I have two Fosgate amps pushing around 2000 watts in my car and the lights do not dim. The only time the alt can not keep up is when I have the radio blasting, lights on, and the fan running at high! I recommend the 3G install.
 

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Discussion Starter #7
everything seems to work good while it is running just when he leaves over night its dead in the morning

i'm wondering if it is a bad diode

and when the batt is unplugged with the motor running it died would this be caused buy the under drive pulleys and week alt

when i get it here today ill check it with a multimeter

i was just checking to see if it was a common prob

thanks for the help
 

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The First thing I would do is check for a parasitic Draw.
With the meter on the Amps reading and everything off. Disconnect the positive cable and put the meter inline. See what it reads. To help to prevent blowing the fuse in the meter from the Amp spike. Put one lead on the terminal and the other on the battery. Then slide the cable off then see what it reads.

Im not sure what the Specs are for the mustang but most cars are like .025 Amp draw.

If it is alot higher then start pulling fuses one at a time and watch the meter. When you see the meter drop then it is on the circuit of the fuse that you just pulled.

This is how I set my meter up.
 

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I had the exact same symtoms when my alt went bad. It is probably a bad diode which is stuck closed I believe it is. It creates a draw while the car is not on, and drains the battery, fix it soon, or it will get really bad, really quick, trust me. You can also check out PA Performance, they have a lifetime warranty, and have lower than a 2% failure rate. If your alternator takes a complete crap, it will take your battery with it, so be prepared...good luck
 
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