Alternator problems

[Silverbullitt]

After 19 years and 85,000 miles the alternator was squealing when cold. Ordered a new Bosch unit. Looks perfect. Installed started the car and the volt meter read zero. Test drove 5 mi and battery voltage was higher after test. Pulled the new unit, replaced with original. Volt meter is reading fine. Returned Bosch unit for another, same result. Returned and sent original to a reputable rebuild shop. Installed and volt meter is now zero.

Is the wiring in a gt alternator different than an 06 5.4 F150 or Explorer? Doing research the alternator is the same part across all three vehicles. I hope I am wrong.

 

[69b302]

Maybe grounding issues with alternator case?

 

[nota4re]

Installed and volt meter is now zero.

Honestly, this is NOT a good way to assess the health of the alternator... especially on a vehicle notorious for faulty gauges.

Use a simple voltmeter to measure voltage at the alternator when the car is running. You should get a reading somehere between 13.5 to 14.5V which would indicate that the alternator is charging. If voltage at the alternator is the same when the car is running as when it is off (nominally ~12.6V) THEN, maybe you have an alternator issue.

More likely to me is that you have a battery nearing end of life and then you are experiencing a well-known issue where one or more gauges are not initializing correctly.

 

[Silverbullitt]

Honestly, this is NOT a good way to assess the health of the alternator... especially on a vehicle notorious for faulty gauges.

Use a simple voltmeter to measure voltage at the alternator when the car is running. You should get a reading somehere between 13.5 to 14.5V which would indicate that the alternator is charging. If voltage at the alternator is the same when the car is running as when it is off (nominally ~12.6V) THEN, maybe you have an alternator issue.

More likely to me is that you have a battery nearing end of life and then you are experiencing a well-known issue where one or more gauges are not initializing correctly.

I’m using an Optima charger/tender 13.3v prior to each test. 2 new alternators set the guage to 0. I put the old one back in prior to getting it “rebuilt” voltage was fine. Get it rebuilt voltage 0. I’m taking the wiring manual and the alternator back to the rebuilder. Hopefully the internal wiring is different in a GT. Still looking online.

 

[JOETWINT]

Check the voltage with a voltmeter at the alternator or the battery like nota4re said. The in dash gauge is most likely not registering (initializing) due to it seeing a spike in voltage from the (new) charging alternators.

 

[Silverbullitt]

Check the voltage with a voltmeter at the alternator or the battery like nota4re said. The in dash gauge is most likely not registering (initializing) due to it seeing a spike in voltage from the (new) charging alternators.

I did something easy. I ordered a voltmeter that plugs into the cigarette lighter. It will tell me all is good until I can get it up to Rich’s shop to diagnose.

 

[nota4re]

OP - we're trying to help here...

A "bad" alternator is NOT going to make the Voltmeter in the car show "0". If a bad alternator is installed, the gauge will show right around 12v when the car is running and ~14v if the alternator is working. If the Voltmeter is showing 0 V, this has NOTHING to do with the alternator but is an indication that the gauge is not working. As I said in my first reply, a low battery WILL cause one or more gauges not to initialize. It is FAR more likely that this is what you are experiencing.

The internals of the Ford GT alternator are wired no differently than any other alternator.

 

[Silverbullitt]

OP - we're trying to help here...

A "bad" alternator is NOT going to make the Voltmeter in the car show "0". If a bad alternator is installed, the gauge will show right around 12v when the car is running and ~14v if the alternator is working. If the Voltmeter is showing 0 V, this has NOTHING to do with the alternator but is an indication that the gauge is not working. As I said in my first reply, a low battery WILL cause one or more gauges not to initialize. It is FAR more likely that this is what you are experiencing.

The internals of the Ford GT alternator are wired no differently than any other alternator.

FIXED!!!! Went back to the rebuilder. They dug deeper and found there are two different rectifiers for the same alternator. The two new ones and the original rebuilt had the wrong one. They still had the original, swapped it and voltmeter is correct now. Thanks for the help guys, but swapping alternators 8 times and digging deeper found the problem. I hope this helps the next guy.

 

[Tomcat]

What part # (alternator) and what is the right rectifier #?
Good find!!!

 

[Silverbullitt]

What part # (alternator) and what is the right rectifier #?
Good find!!!

I’ll check with the rebuilder tomorrow. Sure would save lots of grief for many.

 

[fjpikul]

Good deal. I don't t know why everyone says you're worthless.

 

[B.M.F.]

FIXED!!!! Went back to the rebuilder. They dug deeper and found there are two different rectifiers for the same alternator. The two new ones and the original rebuilt had the wrong one. They still had the original, swapped it and voltmeter is correct now. Thanks for the help guys, but swapping alternators 8 times and digging deeper found the problem. I hope this helps the next guy.

Congrats!

I pretest all my alternators or customers alternators on a test bench prior to putting them in a car.

 

[PeteK]

Silverbullitt: Excellent info. Thanks for adding to the knowledge base.