Battery light come on randomly - Mustang Evolution

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Old 12-25-2012, 04:43 PM   #1
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Battery light come on randomly

Merry Christmas everyone

As the title says my battery light comes on at random times whether it be idling, cruising, or hard acceleration. I never noticed the voltage gauge drop or anything like that. I do have Steeda underdrive pulleys on though.

Thanks for any help!!
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Old 12-25-2012, 04:57 PM   #2
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Make sure you're P and N are tighten I had the same problem
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Old 12-25-2012, 04:59 PM   #3
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Most likely your alternator is going out.
The diodes can start going bad and it causes your battery light to come on.
Go get it checked thoroughly and replace it.
Mine did this for a month or 2 until I figured it out.
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Old 12-25-2012, 05:00 PM   #4
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And if its not that get you're batt checked out
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Old 12-25-2012, 05:40 PM   #5
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Quote:
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Make sure you're P and N are tighten I had the same problem
Thanks. They're good and tight. But haven't had a chance to have the battery checked out.
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Old 12-25-2012, 05:44 PM   #6
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Quote:
Originally Posted by BackPressure View Post
Most likely your alternator is going out.
The diodes can start going bad and it causes your battery light to come on.
Go get it checked thoroughly and replace it.
Mine did this for a month or 2 until I figured it out.

Agree! it hapen to me couple years ago... don`t take any chance, go to see an electronic sp├ęcialist who got the machine to check your alternator!
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Old 12-25-2012, 05:45 PM   #7
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Quote:
Originally Posted by BackPressure View Post
Most likely your alternator is going out.
The diodes can start going bad and it causes your battery light to come on.
Go get it checked thoroughly and replace it.
Mine did this for a month or 2 until I figured it out.
I bought the car back in July and the dealer said they replaced the alternator when the previous owner traded it in bc it was bad but didnt say why. I have read that it could be due to underdrive pulley on the alt. and that to fix this issue is to go with a higher amp alternator or put stock pulley back on. But I'm not sure I couldn't find a straight answer as to what could fix this issue.
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Old 12-25-2012, 06:12 PM   #8
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Factory was 130A. You can run a 110A (I do because I never use my stereo and I didn't want to wait 2 weeks for a 130 to ship), so I'd imagine UDs would be fine as long as you have a respectable brand (BBK or Steeda).
I'd still go test your alternator; rule 1 of dealerships is they're full of sh1t and ignore anything they tell you about your vehicle unless it comes directly from the mechanic that worked on your vehicle.
Source: good friends that are dealer mechanics.

The mechanic may write "small clog in air filter" and the service writer tells you that your intake was completely jammed and he's surprised the car ran.
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Old 12-25-2012, 06:19 PM   #9
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mine has been doing the same thing, battery is almost two years old and original alternator 98,000 miles
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Old 12-25-2012, 06:20 PM   #10
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Quote:
Originally Posted by BackPressure View Post
Factory was 130A. You can run a 110A (I do because I never use my stereo and I didn't want to wait 2 weeks for a 130 to ship), so I'd imagine UDs would be fine as long as you have a respectable brand (BBK or Steeda).
I'd still go test your alternator; rule 1 of dealerships is they're full of sh1t and ignore anything they tell you about your vehicle unless it comes directly from the mechanic that worked on your vehicle.
Source: good friends that are dealer mechanics.

The mechanic may write "small clog in air filter" and the service writer tells you that your intake was completely jammed and he's surprised the car ran.
That's true good point, I am running Steeda UDPs but I'm definitly going to get my alternator checked soon.

Thank you.
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Old 12-25-2012, 06:20 PM   #11
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mine has been doing the same thing, battery is almost two years old and original alternator 98,000 miles
Your alternator has a failing diode, replace it.

---------- Post added at 07:20 PM ---------- Previous post was at 07:20 PM ----------

Quote:
Originally Posted by Perricanfalcon View Post

That's true good point, I am running Steeda UDPs but I'm definitly going to get my alternator checked soon.

Thank you.
Glad to help!
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Old 12-25-2012, 06:27 PM   #12
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Many, many generators are replaced each year because of bad connections between the generator and the battery (both +12 V and ground) and because of bad batteries.

With the engine running check the voltage between the generator output terminal and the battery positive post. In an ideal would it would be 0.0 V, but in our real world it may be as much as 0.3 V--anything more means the wiring/connectors ar bad;

Then check the voltage between the generator body and the negative battery terminal. Again, 0.0 V would be perfect but anymore than 0.3 V means there is a ground problem. Check the main ground strap from the battery to the block (just behind the oil filter adapter), it often comes loose and/or gets corroded.

Make sure the battery terminal connectors are both clean and tight. Tight is nice but a layer of corrosion between the battery post and the connector will create problems regardless of how tight the connection is.

Have the battery load tested with a 250 A or better tester. The handheld testers used by the FLAPS are nice, convenient and quick, go/no go testers however they are no replacement for a REAL wire resistor or carbon pile tester that places a high-amp load on the battery for 15 to 30 seconds...
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