What Would Cause an Alternator/Voltage Regulator to Fail Twice?

[Erik]

I had the lower fuel injector gaskets replaced recently. As it was not a job I wanted to undertake myself, I had a Corvette specialist dealer who still had some ZR1 knowledge do the job. On the way back home, about an hour into the drive, thr battery light came on and the voltage gauge dropped down. I'd had the alternator tested twice in the years before, and it had always passed with flying colours. The bearing had been a bit noisy, so that got replaced. But, as it was 30 years old, and the ZR-1 under hood area isn't friendly to things electronic, I wasn't too surprised. Took it back, they had the alternator rebuilt, and I was back on the road again. Survived the trip back this time, and all seemed ok.

Tonight, was on the way to the local car show, and the dash lights and Instrument panel flashed briefly. Weird, but all seemed ok and kept driving. About a minute later, I noticed the battery light was on and the gauge was showing low. Crap. Still running fine, but just off the battery.

So, as it wasn't a problem before the plenum pull, and I'm not a huge believer in coincidences, I'm wondering what could they have done that would cause the voltage regulator to blow twice? And seeing as how the plenum was off for some extensive work, I'd guess it was something there.

Any thoughts before I call the shop and start yelling?

[Erik]

Made it home just fine and the car was running like a champ. Except for the charging part?

[Mikey]

Are you sure you have a good connection to the regulator? Particularly the voltage excitation wire?

[Erik]

Originally Posted by Mikey

Are you sure you have a good connection to the regulator? Particularly the voltage excitation wire?

Nope! Not at all.
What should I be checking on?

[Mikey]

You should see a small wire that has 12 V with ignition on that goes to the regulator. You can disconnect the plug and check the pin in the harness. Also watch the voltmeter gauge does it show around 14 V when the car is running? If not then does wiggling the wire excitation wire plug change the behavior at all?

[DRM500RUBYZR-1]

Sounds like the original problem is still the problem.

If there are any looses connections starting at the battery and working out, that could cause a correctly functioning alternator to fail in charging the battery.
The flash that you observed suggests some type of voltage interruption.

Being as the problem did not exist before the work, i would carefully review every electrical connection and wire that would have been disturbed during the work as well as both battery cable connections.

Let us know what you find or do not find.

Marty

[Erik]

Originally Posted by Mikey

You should see a small wire that has 12 V with ignition on that goes to the regulator. You can disconnect the plug and check the pin in the harness. Also watch the voltmeter gauge does it show around 14 V when the car is running? If not then does wiggling the wire excitation wire plug change the behavior at all?

It dropped down to about 11. Though the gauge isn?t that accurate anyway. One of those times that I wish they had just kept the digital dash of the pre-90s.

[Erik]

Well, stuff just gets more interesting. I had a meet to go to, 10 minutes away from the house, and as the corvette was drivable, I gave it a full charge last night and headed out this morning. Dammit, if the gauge wasn?t showing it was charming as normal, and the battery light was off. Wtf?

So my first thought is, perhaps my first alternator didn?t fail. Maybe when they were working o]under the plenum, they disturbed some wiring or something, and that caused the issue. Replace alternator with new one, wiring gets messed with again, works for a while and then disconnects again.

So what would cause this scenario? Car runs fine. Drives well off the battery, but alternator doesn?t charge. I?ve seen some comments about the alternator pigtail getting wonky. Negative battery cable? Any other thoughts?