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Discussion Starter · #1 ·
This is the second new battery I have put in my 1989 Mustang GT since last October.

I was driving it home one day and my volts went past the 18V mark.

I keep thinking it's my alternator.

is there anything else i am over looking?
 

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It sounds like the voltage regulator in the alternator is going bad or the wiring for the reference voltage is bad (I don't have a diagram in front of me so don't know what connection or wire that is if any). Too high of a voltage from the alternator will over charge and eventually kill a battery, it's not instant though and the battery can take some abuse. Sometimes they actually bulge and leak when that happens. What is the voltage (measured with a handheld voltmeter) across the battery with the car running? Pull out the two plugs on the side of the alternator and inspect for any burning, corrosion, or crusty brittle stuff on the lugs and the plugs.

I'm not a fan of swapping random parts but an alternator and the main power pigtail is cheap and easy to replace. Swapping over to a 3G style alternator is a much better plan and much safer when done correctly.
 

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Discussion Starter · #3 ·
It sounds like the voltage regulator in the alternator is going bad or the wiring for the reference voltage is bad (I don't have a diagram in front of me so don't know what connection or wire that is if any). Too high of a voltage from the alternator will over charge and eventually kill a battery, it's not instant though and the battery can take some abuse. Sometimes they actually bulge and leak when that happens. What is the voltage (measured with a handheld voltmeter) across the battery with the car running? Pull out the two plugs on the side of the alternator and inspect for any burning, corrosion, or crusty brittle stuff on the lugs and the plugs.

I'm not a fan of swapping random parts but an alternator and the main power pigtail is cheap and easy to replace. Swapping over to a 3G style alternator is a much better plan and much safer when done correctly.

Thanks for the help.... I'm broke with a baby on the way so i'm getting the lifetime warranty referbished stock replacement alternator for 99 bucks. but I would rather have a 130amp alternator though.

but my battery had some pressure release that came out the top of the battery, it shorted out my drivers side headlight too
 

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Thanks for the help.... I'm broke with a baby on the way so i'm getting the lifetime warranty referbished stock replacement alternator for 99 bucks. but I would rather have a 130amp alternator though.

but my battery had some pressure release that came out the top of the battery, it shorted out my drivers side headlight too
Sounds like it was overcharing for a while.
Last time I bought one it was like $60, must have been a few years ago. Either way.... Make sure you inspect those pigtail connectors. It is a shitty design by Ford, both of my foxes had small fires from those piece of **** connectors getting corroded and overheating. You should replace at least the large pigtail connector when you replace the alternator regardless of its condition.

If it were me, I'd remove the battery and clean all around and under that battery area by getting the area a little wet and sprinkling some baking soda around, let it sit for a few minutes and rinse it off.
 

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Discussion Starter · #5 ·
Sounds like it was overcharing for a while.
Last time I bought one it was like $60, must have been a few years ago. Either way.... Make sure you inspect those pigtail connectors. It is a shitty design by Ford, both of my foxes had small fires from those piece of **** connectors getting corroded and overheating. You should replace at least the large pigtail connector when you replace the alternator regardless of its condition.

If it were me, I'd remove the battery and clean all around and under that battery area by getting the area a little wet and sprinkling some baking soda around, let it sit for a few minutes and rinse it off.
alright, i'll get the new pigtail as well. and wash the battery area. I haven't put the new battery back in yet so that shouldn't be to hard.

great info though, thank you.

this may sound dumb but the pigtail is the wires connected directly to the back of the alternator right?

what do i need to get the belt off?
i'm guessing a long breaker bar or something?
 

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A breaker bar and socket on the tentioner bolt or, I just use the stock tire iron or a random piece of something long. Shove the pointy end in between the pulley and the upper part of the tensioner and push the top to your left, it takes just seconds.

The pigtail of concern is the connector with the two large black/orange striped wires and some other small wire on the alternator. 1986-93 Mustang Alternator Rectifier Plug by PA Performance at LRS - Same Day Shipping!. Autozone said they didn't carry it but I found it hanging on the shelf with the other electrical stuff.

Do you already have the new alt? If not take your old one to compare. That same 2G alternator part number is used in a lot of Fords but the housing is clocked differently for different vehicles (120 degrees off).
 

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Discussion Starter · #7 ·
A breaker bar and socket on the tentioner bolt or, I just use the stock tire iron or a random piece of something long. Shove the pointy end in between the pulley and the upper part of the tensioner and push the top to your left, it takes just seconds.

The pigtail of concern is the connector with the two large black/orange striped wires and some other small wire on the alternator. 1986-93 Mustang Alternator Rectifier Plug by PA Performance at LRS - Same Day Shipping!. Autozone said they didn't carry it but I found it hanging on the shelf with the other electrical stuff.

Do you already have the new alt? If not take your old one to compare. That same 2G alternator part number is used in a lot of Fords but the housing is clocked differently for different vehicles (120 degrees off).
yeah, i'm taking the old one in first. Also because I don't wanna pay the core charge of 30 bucks or whatever it is.

I think i'm gotta check out some cheap breaker arms because if I use the tire iron, knowing my luck i would screw something up real bad using the tire iron.
 

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doint know about your area,but a 130 amp 3g is $30 bucks at the boneyard. if you have a major wealding supply store in your area you can buy 4 ga wire for about $1.20 a ft.
 

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Discussion Starter · #10 ·
I just use the socket with ratchet, and use the tube from the jack
I don't have a jack lol hard to beleave huh.

and the idea for getting a alternator from a junk yard doesn't sound to great an I don't wanna fart with rebuilding either. an the one from auto zone has a limited lifetime warranty....
 

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if you was close i'd give you the BRAND NEW REBUILT stock autozone alt i bouaght and used for three weeks , and then replaced with a j/y alt. that 65 amp alt wouldnt have a chance against my mark viii fan, big sterio, and u/d pullys! i'm just saying. i'll run a $30 3g alt before i ever put that 65 amp brand new alt on that i have in my shed!
 

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Discussion Starter · #12 ·
if you was close i'd give you the BRAND NEW REBUILT stock autozone alt i bouaght and used for three weeks , and then replaced with a j/y alt. that 65 amp alt wouldnt have a chance against my mark viii fan, big sterio, and u/d pullys! i'm just saying. i'll run a $30 3g alt before i ever put that 65 amp brand new alt on that i have in my shed!
That's really good of you.

Thank you.

I'm at that point were I just wanna get it running like it should ya know?
I don't have any stereo system or u/d pulleys so the stock deal should work great for me for now.
 

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dude , you need to get some tools ! even if its a $50 set of stanleys from wally world. spend $60 and they have a pretty good set there, damn foxes are old.
 

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Discussion Starter · #14 ·
dude , you need to get some tools ! even if its a $50 set of stanleys from wally world. spend $60 and they have a pretty good set there, damn foxes are old.
I have some basic tools, but it seems like anything that goes wrong with my fox, needs some special tool that I don't have.
 

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Discussion Starter · #15 ·
What size is the nut that you put the socket on to move the belt tensioner?

I've tried 17 mm, 19 mm, 3/4, and 11/16.

Is there a size between 3/4 and 11/16?
 

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Discussion Starter · #18 ·
well guys i played the PA lottery an only won enough to pay for my ticket so I wont be getting my mustang completely redone this time lol... :/
 

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Discussion Starter · #19 ·
Got my new alternator and the big pigtail.
I hope this all works well.

Thanks for all your help.
 
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