Bad Alternator?

Discussion in 'SN95 4.6L Mustang Tech' started by JamesD87, Mar 24, 2014.


  1. JamesD87

    JamesD87 Member

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    Alright so my battery died the other day randomly. I didn't leave any lights on or anything like that. I thought maybe there was a short somewhere but cant find one. I was thinking it was the alternator so I got online and started doing some research. I read something that said to start your car and unhook the battery and if the car dies its your alternator. So I went out there and with a booster box I jumped the car. I went to unhook the booster box and the car died...I didn't even have to unhook the battery. Is this test accurate and does it sound like that's the problem...my alternator? Thanks guys.
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  2. wmburns

    wmburns SN Certified Technician

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    For today's cars

    No battery = No Alternator.

    The first test should be the battery and battery cables. This is a PRIME symptom of a bad battery. IE, the motor randomly dies and then restarts OK.

    Then have the alternator tested for correct output and excessive AC ripple (bad diode).

    Bottom line. Today's cars simply will not run right without a strong battery and charging system.

    The disconnect the battery to test the alternator test is a relic from the old days. The days when 30 amp alternators were the norm. Today's 100 amp alternators are different which is why the battery is so important.
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  3. JamesD87

    JamesD87 Member

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    I'm pretty confident the battery is good...I bought it brand new about 2 weeks ago...do I need to remove the alternator for it to be tested or can that be done without removing it?
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  4. Mattstang04

    Mattstang04 Active Member

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    If the car is driveable, take it to almost any local autoparts store. Autozone, Advance, O'Reilly's, Napa, etc. They are easily tested on the car. Have them double check that battery too.
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  5. JamesD87

    JamesD87 Member

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    Just an update...I bought a new alternator that I found online and installed it Friday and all my problems have since gone away.
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