Alternator fuse keeps blowing

1998 FORD MUSTANG
125,477 MILES • 4.6L • V8 • 2WD • MANUAL
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BRIDGES77
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Battery light came on one day. About a week later it shut off on the way to work. Found the alternator fuse blown. Replaced the alt thinking it was inside the regulator. Also changed out the starter and battery. Fuse blew again. It blows at different times so hard to tell what’s going on. Please help
Dec 28, 2019 at 12:09 PM
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ASEMASTER6371
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Good afternoon.

What is the fuse number that keeps failing?

Roy
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Dec 28, 2019 at 1:22 PM
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BRIDGES77
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The alternator fuse here bottom left corner.
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Dec 29, 2019 at 9:07 AM
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ASEMASTER6371
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Can you please give me the fuse number? It is way too small to read on that picture.

Roy
Dec 29, 2019 at 9:13 AM
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BRIDGES77
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I think it is #14. It is under the hood fuses. Takes a 20 amp fuse and is labeled alt.
Dec 29, 2019 at 9:29 AM
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ASEMASTER6371
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Okay, check the yellow wire at the alternator. Does it have power with the key on?

If it does not, then we are at the issue. If you have replaced the alternator, then either the alternator is bad again, which I doubt, or you have a wiring issue.

Roy

Dec 29, 2019 at 9:41 AM
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BRIDGES77
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Unfortunately the battery is dead now. I would have to get back to you with that info. So if no power at the yellow wire, would that be the wire to inspect inside the loom for a short to ground?
Dec 29, 2019 at 9:50 AM
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ASEMASTER6371
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That is correct. That fuse only controls that wire from the fuse box to the alternator.

Roy
Dec 29, 2019 at 9:54 AM
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BRIDGES77
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Sweet and that is why it won’t charge the alternator? Thanks
Dec 29, 2019 at 10:23 AM
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ASEMASTER6371
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Correct.

Roy
Dec 29, 2019 at 10:29 AM
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BRIDGES77
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Thank you so much!!!
Dec 29, 2019 at 10:29 AM
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ASEMASTER6371
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You are welcome.

Always glad to help.

Roy
Dec 29, 2019 at 10:32 AM
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BRIDGES77
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Update. The battery is charged now. Key on or off it instantly blows the fuse.
Jan 13, 2020 at 2:26 PM
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ASEMASTER6371
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Okay, do the checks I suggested before you charged the battery.

Roy
Jan 13, 2020 at 2:49 PM
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BRIDGES77
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Say what?
Jan 13, 2020 at 2:53 PM
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BRIDGES77
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I charged the battery then tried to do the test. No power at the yellow wire but the fuse is blow and keeps blowing as soon as I put one in.
Jan 13, 2020 at 2:58 PM
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ASEMASTER6371
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Disconnect the yellow wire from the alternator and see if the fuse still fails.

Roy
Jan 13, 2020 at 3:24 PM
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BRIDGES77
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With the yellow wire unhooked it does not blow now.
Jan 13, 2020 at 3:49 PM
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ASEMASTER6371
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Do you have power to that wire with it disconnected?

Roy
Jan 13, 2020 at 4:08 PM
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BRIDGES77
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Yes about 9. volts?
Jan 13, 2020 at 4:17 PM
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ASEMASTER6371
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You should have battery voltage. If your battery is charged, it should be 12.6 volts.

If you hook that wire up, and the fuse fails, it points directly to the alternator.

What brand alternator did you use to replace it?

Where did you buy it?

Roy
Jan 13, 2020 at 4:26 PM
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BRIDGES77
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Standard replacement from O'rielly Auto parts. This is the second one. My original was from American Muscle, I thought it was the alternator too?
Jan 13, 2020 at 4:28 PM
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ASEMASTER6371
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If the fuse does not fail with it disconnected, that means the wiring is good up to the alternator.

Roy

Jan 13, 2020 at 4:31 PM
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BRIDGES77
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It is possible that the yellow wire and green/red were switched? The pig tail for the alt was replaced thinking this was the initial cause to the blown fuse, would it matter?
Jan 13, 2020 at 4:49 PM
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ASEMASTER6371
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Yes, it would. Look at the diagram I attached back in the beginning. It identified the wires and where they were located in the connector.

I also attached the diagram of the connector for you as well.



Roy
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Jan 13, 2020 at 5:03 PM
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BRIDGES77
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Okay, I definitely just made the wires match the last pic, they were swapped. The old connector fell apart so I had to replace it.
Jan 13, 2020 at 5:15 PM
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BRIDGES77
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Ok I definitely just made the wires match the last pic, they were swapped. The old connector fell apart so I had to replace it.
Jan 13, 2020 at 5:15 PM
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ASEMASTER6371
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Good find.

Let us hope all is good.

Roy
Jan 13, 2020 at 5:19 PM
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BRIDGES77
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Would a failing alternator connector cause the blown fuse in the first place?
Jan 13, 2020 at 5:25 PM
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ASEMASTER6371
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If the wires were not in the right position, yes. It may have been going to a direct ground causing the fuse to fail.

Roy
Jan 13, 2020 at 5:33 PM
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BRIDGES77
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Awesome thank you so much for your help again. Have a blessed day!
Jan 14, 2020 at 2:57 AM
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ASEMASTER6371
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You are welcome.

Always glad to help.

Roy
Jan 14, 2020 at 3:03 AM