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5.0L (1979-1995) Mustang Technical discussions on 5.0 Liter Mustangs within. This does not include the 5.0 from the 2011 Mustang GT. That information is in the 2005-1011 section.

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Old 05-20-2007, 10:49 PM   #1
86onboost
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Default Alternator Help! battery wont stay charged

i had my mustang with a stock alternator, for a while, and the batter wouldnt stay charged. i would cut on the car, and disconnect the battery, and it would cut off, (bad altenator)

well i got myself a new 75amp alternator, and still the same thing, it wont keep the batter charged, we tried optima batterys and duralast, still the same.

Why wont my battery stay charged. Do i need a bigger amperage, or is there a special way to connect it.

BTW its the alternator with the plug, i tried one with a single wire, but still no luck.
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86 notchback ( coupe) 302 small block, with .040 pistons, everything else stock.

this is will be a drag car and a project car everything tooken off, like the a/c, heater, windshield wiper, power steering ect. 15x3 front weld skinny.
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Old 05-20-2007, 10:50 PM   #2
AdderMk2
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Default RE: Alternator Help! battery wont stay charged

disconnecting the battery to test the alternator... is probably what killed it



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Old 05-21-2007, 12:00 AM   #3
86onboost
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Default RE: Alternator Help! battery wont stay charged

we also went to autzone, and the test was positive, but the car is supposed to stay on when the battery is disconnnected.

and the battery wont keep charge, we tried numerous of batteries.

we tried 2 plug alternators, and 1wire one, and still no luck.

do you think its the amp size , maybe 75 aint enough

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86 notchback ( coupe) 302 small block, with .040 pistons, everything else stock.

this is will be a drag car and a project car everything tooken off, like the a/c, heater, windshield wiper, power steering ect. 15x3 front weld skinny.
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Old 05-21-2007, 12:13 AM   #4
foxstang89
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Default RE: Alternator Help! battery wont stay charged

do you have underdrive pullies, a simple question but you never know
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Old 05-21-2007, 12:17 AM   #5
86onboost
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Default RE: Alternator Help! battery wont stay charged

yes , i am supercharged, i have the supercharge pulley, crank pulley, alternator pulley ( relocated to bottom) and water pump pulley, thats all i running
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86 notchback ( coupe) 302 small block, with .040 pistons, everything else stock.

this is will be a drag car and a project car everything tooken off, like the a/c, heater, windshield wiper, power steering ect. 15x3 front weld skinny.
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Old 05-21-2007, 12:29 AM   #6
samseed101
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Default RE: Alternator Help! battery wont stay charged

When the car is running, what does your voltage look like?

And did you say you had underdrive pulleys with a supercharger? Your answer was kind of confusing.
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Old 05-21-2007, 12:41 AM   #7
86onboost
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Default RE: Alternator Help! battery wont stay charged

what im sayin is that the only pulleys i have is supercharger, alternator, water pump, and crank
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86 notchback ( coupe) 302 small block, with .040 pistons, everything else stock.

this is will be a drag car and a project car everything tooken off, like the a/c, heater, windshield wiper, power steering ect. 15x3 front weld skinny.
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Old 05-21-2007, 01:07 AM   #8
86onboost
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Default RE: Alternator Help! battery wont stay charged

also the amp i got was a 75 alt. from autzone.

maybe i connected something wrong, can anyone post on how to corretly install an alternator ( the one with the plug)
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86 notchback ( coupe) 302 small block, with .040 pistons, everything else stock.

this is will be a drag car and a project car everything tooken off, like the a/c, heater, windshield wiper, power steering ect. 15x3 front weld skinny.
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Old 05-21-2007, 01:25 AM   #9
86onboost
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Default RE: Alternator Help! battery wont stay charged

anyone?
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86 notchback ( coupe) 302 small block, with .040 pistons, everything else stock.

this is will be a drag car and a project car everything tooken off, like the a/c, heater, windshield wiper, power steering ect. 15x3 front weld skinny.
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Old 05-21-2007, 01:29 AM   #10
preciousroy
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Default RE: Alternator Help! battery wont stay charged

75 is a bit low, try a 130 amp from an sn95
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Old 05-21-2007, 01:29 AM
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