Alternator fuse keeps blowing

Hi,

I want to confirm which fuse is blowing. I assume it is the 20 ALT fuse. If I am correct, disconnect the battery and check to see if there is continuity to ground from the yellow/white wire at the alt. (See pic 1) I attached what I have as far as a schematic as well.

Here are a few links you may find helpful:

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

https://www.2carpros.com/articles/how-to-use-a-voltmeter

https://www.2carpros.com/articles/how-to-check-wiring

If it is blowing as soon as you put the fuse in, there is a dead short to ground. So, confirm none of the pins in the new connector are damaged. I suspect the yellow/white wire is toughing a ground point.

Let me know.

Joe

You are very welcome. Let me know what you find. Since it is blowing the fuse immediately, I suspect there is a short in that wire or internal in the alternator. You could disconnect that wire from the alt to see if it still blows if you suspect it is internal.

Let me know.
Joe

Thanks for visiting 2CarPros.

Yes, the alternator can short internally and cause this. It is not uncommon if these are re-manufactured units. I would also suggest replacing the pigtail to the alternator if you haven't already. The new ones usually come with the pigtail.

Something is shorted internally. If this is a remanufactured alt, get a different brand. I always get a new one. It doesn't have to be an OEM alt, but I never have luck with the remanufactured ones. Was this replacement remanufactured?

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Here is a link that explains removal and replacement in general

https://www.2carpros.com/articles/how-to-replace-an-alternator

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Directions from alldata / Pic 1 correlates with the directions.

REMOVAL
1. Disconnect battery ground cable.
2. Disconnect the wire harness attachments to the generator (GEN) and voltage regulator.
3. Disengage the generator drive belt from the generator pulley.
4. Remove retaining bolts and generator mounting bracket.
5. Remove the mounting bolts and the generator.

INSTALLATION
1. Position the generator on the engine.
2. Install the generator mounting bolts. Tighten bolts to 20-30 N.m (15-22 lb-ft.).
3. Install generator mounting bracket and retaining bolts. Tighten bolts to 8-12 N.m (71-106 lb-in).
4. Install the drive belt over the generator pulley.
5. Connect the voltage regulator wiring and output wire to the generator and voltage regulator. Tighten output terminal nut to 7-9 N.m (62-79 lb-in).
6. Connect battery ground cable.

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If he saw the short in the alternator, something has failed. Remove the alt and have it bench tested at the parts store. If it is bad (and I believe it is), get a different brand and if possible, stay away from the remanufactured ones.

Let me know if this takes care of the problem.

Take care,
Joe

I say it is the alternator. Something internal may have come apart causing a direct short to ground. Since your friend saw a spark in the alternator, that is most likely where the problem is located.

Let me know the results of the bench test.

Joe

You are very welcome and I couldn't agree more with you. New parts are bad more often than people know. When it comes to electronics, such as this, it is a good idea to spend a couple more dollars and get something good.

Take care of yourself and let us know if you need help in the future.

Joe

Happy to help.

Hi,

Disconnect the alternator (make sure to shield the power wires from shorting) and plug the fuse in to see if it still blows.

Let me know.

Joe

Hi,

Then it's not the alternator. I suspect (since it was disconnected) the problem is between the fuse and alternator.

Take a look at the attached pic. (Note I am looking at a GT model 4.6L) Note that the power comes from the battery to the fuse, through the fuse, and into the yellow wire with a white tracer and then to the alternator.

So, if with the alternator disconnected that fuse blows, it has to come after the fuse which is the aforementioned wire. You need to check to see if it is shorted to ground. Check the wire, the connector, and everything you can on that wire. Or, with the battery disconnected, check to see if there is continuity to ground in that wire. There shouldn't be if it is disconnected.

Let me know what you find.

Joe

That leads me to believe the short is either in the connector or the alternator itself. Check the plug to make sure none of the pins are damaged, bent, as well as on the alternator.

If the wiring is good, then I would replace the alternator.

Let me know.
JOe

Sounds good. Let me know what you find. I'm interested in knowing if that is where the problem is.

Take care,
Joe