Alternator Bench Test Results Messages Definition?

[Julian]

Hi,

Wonder if any pros here can help me out. My 89 Mustang GT stopped charging the battery. I did all the recommended voltage tests (without going in to detail) and finally took the alternator out and took it to 3 different parts stores for testing. All 3 said the alternator failed, but no one knew the test equipment well enough to interpret the results.

All stores’ bench test machines failed the alt before they could get it spun up to speed. They’d try to spin and stop the test. However, the pulley spins freely just fine.

The NAPA machine showed: Light circuit result: FAILED
Autozone machine showed: Line voltage dropped below 90V

Have any of you seen these messages? Any way to point to the alternator specifically or only the voltage regulator for failure?

Thanks!
Julian

Topic

[college man]

Don’t put your faith in these bench test machines. Check the output voltage in the car.
Also check the battery. More in this link.

http://www.ericthecarguy.com/faq/solving-automotive-electrical-problems

[Julian]

Just to finally follow up to this thread. After taking my bad Alternator to 2-3 different stores for testing, I was convinced it was dead. I didn’t want to spend the money to see if it was just the voltage regulator or the whole alt.
In general, it was a shortcoming of 87-93 Mustangs to have an under-powered alt (75 Amp). Further, from the factory, the mustangs came with incorrectly sized wires for the alt that had a history of burning up. Anyway, I upgraded my alt to a 130 amp with 4 gauge wires and the problem was resolved.

[college man]

[quote=”juels98″ post=186709]Just to finally follow up to this thread. After taking my bad Alternator to 2-3 different stores for testing, I was convinced it was dead. I didn’t want to spend the money to see if it was just the voltage regulator or the whole alt.
In general, it was a shortcoming of 87-93 Mustangs to have an under-powered alt (75 Amp). Further, from the factory, the mustangs came with incorrectly sized wires for the alt that had a history of burning up. Anyway, I upgraded my alt to a 130 amp with 4 gauge wires and the problem was resolved.[/quote]

Glad you resolved it. 🙂

[Bluesnut]

An alternator rated at 75 amps should be more than enough for your Mustang unless you have it loaded down some very high watt amps and so on.

[Author]

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