Electrical 1982 Mustang 5.0 Alternator wiring help NEEDED

2000HeadlessGT

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Feb 27, 2012
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I have a 82 Mustang GT and for some reason the battery won't stay charged. I had the battery tested and replaced and its good, I also had the alternator tested and its good also.
I used a volt meter and with the car off the battery is 12v and when the car running the battery drops to 7 volts. Im pretty sure the wiring on the alternator is wrong. Can someone please show me how it should be wired up because from the looks of it its not charging the battery at all. Any help will greatly be appreciated. Also its the factory alternator.
 
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Hudson N

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Aug 7, 2018
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Queen creek Arizona
I have a 82 Mustang GT and for some reason the battery won't stay charged. I had the battery tested and replaced and its good, I also had the alternator tested and its good also.
I used a volt meter and with the car off the battery is 12v and when the car running the battery drops to 7 volts. Im pretty sure the wiring on the alternator is wrong. Can someone please show me how it should be wired up because from the looks of it its not charging the battery at all. Any help will greatly be appreciated. Also its the factory alternator.
I had the EXACT same thing happen to me. The problem turned out to be the cluster, the battery light is part of the charging circuit, I pulled my cluster and the ribbons on the back of the cluster that go to the battery indicator lamp were a bit mangled, I managed to fix them and carefully reconnect the cluster. After that it worked fine. If you still have the problem it's worth checking the harnesses that connect to the alternator. Those go bad pretty easy.
 

Rcdgl

Member
Feb 19, 2018
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x2 on the above, but if you have 12 v at the battery and less when running, that really sounds like the alternator. I had one fail where one of the three diodes died. 12 v off, 11.9 v running. Took a week to figure it out.