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Keeps blowing the 80-amp alternator fuse?

Tiny
CWEIDNER
  • MEMBER
  • 1991 TOYOTA CAMRY
  • 0.5L
  • 4 CYL
  • 2WD
  • MANUAL
  • 250,000 MILES
Tested alternator it was fine. Start car and fuse blows. I just replaced alternator about 6 months ago.
Sunday, September 25th, 2022 AT 7:39 PM

7 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

does the fuse only fail when the engine is started or as soon as it is replaced? If it happens after starting, remove the alternator and have it bench-tested. There could be an issue with the voltage regulator allowing too much power to be supplied to the battery.

I attached the wiring schematic for the charging circuit below. I circled the fuse I believe you are referring to. If that is incorrect, let me know.

Also, if the fuse fails as soon as it is installed, disconnect the connector at the alternator to see if it still blows when a new one is installed. If it doesn't, chances are we either have a short at the alternator connection or internally in the alternator

Take care and let me know what you find.

Joe

See pic below.
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Sunday, September 25th, 2022 AT 8:45 PM
Tiny
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It happened while driving. I had the alternator tested and they said it was working. I replaced the fuse, and it was doing fine until I drove it about 20 feet and the fuse blew again.
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Monday, September 26th, 2022 AT 11:58 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

I understand. Have you been able to inspect the two white wires at the alternator for evidence of damage or an issue with the connection?

Also, if you disconnect the connector at the alternator, does the fuse still fail?

Let me know.

Joe
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Monday, September 26th, 2022 AT 6:45 PM
Tiny
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Fuse does not blow with alternator disconnected. I am in the process of trying the wires and looking for damage.
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Monday, September 26th, 2022 AT 6:54 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

Sounds like a plan. Check the connector as well to make sure the pins aren't touching due to excessive heat.

Let me know what you find.

Joe
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Monday, September 26th, 2022 AT 7:47 PM
Tiny
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Could a bad voltage regulator cause this problem due to the fuse not blowing while idling? But does when I drive it and accelerate the car.
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Saturday, October 1st, 2022 AT 9:59 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,885 POSTS
Hi,

Yes, that can be the cause. If you hook up a multimeter or voltmeter at the battery, it should read approx 14v when running at idle. See what happens if you rev the engine and hold it at approximately 2,000 RPMs.

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Let me know what you find.

Joe
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Saturday, October 1st, 2022 AT 2:31 PM

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