88 Gl ea82, aka mountain grizzly mk2. 

This week on my way home from the garage, I noticed my voltage gauge was just below 12v. Made it home with a dead battery. I figured I would replace the alt the following day, but I'm not sure if the spare I have here is good.

My problem seems to be more than the normal failed alternator though. When the key is turned to run, I have no warning lights at all. I've checked all the fuses and fuse links with my power probe and everything checks out. I have a good ground at the alt, battery, and to the body. I swapped on a spare alt, and still have the same issues. I have battery voltage at both pins at the alt, and at the main charge cable. The battery is new, as are the terminals. 

Am I missing something here? I have a maxima alt on order, but it won't be in for a few days. Even if it turns out this is a wiring issue, I don't mind swaping in an upgrade. This car has 290k on it, and I have no idea if it is still wearing it's factory alternator. 

Every OEM alternator [I've had several] I have ever had wore out one of the field brushes around 150K miles.

The Alternator light never came on, except if you were in total darkness, at idle, with the lights of, sometimes it would glow dimly.

Using a test voltmeter, put the probes on the battery.  with the engine running, you should see around 14V if it is charging.  Anything under 13.8 is not charging.

Battery at rest [rest means no load or charge for at least 24 hours]

12.0V is fully discharged.  12.6V is fully charged.

 

11 hours ago, GrizzlyFox said:

88 Gl ea82, aka mountain grizzly mk2. 

This week on my way home from the garage, I noticed my voltage gauge was just below 12v. Made it home with a dead battery. I figured I would replace the alt the following day, but I'm not sure if the spare I have here is good.

My problem seems to be more than the normal failed alternator though. When the key is turned to run, I have no warning lights at all. I've checked all the fuses and fuse links with my power probe and everything checks out. I have a good ground at the alt, battery, and to the body. I swapped on a spare alt, and still have the same issues. I have battery voltage at both pins at the alt, and at the main charge cable. The battery is new, as are the terminals. 

Am I missing something here? I have a maxima alt on order, but it won't be in for a few days. Even if it turns out this is a wiring issue, I don't mind swaping in an upgrade. This car has 290k on it, and I have no idea if it is still wearing it's factory alternator. 

Not really.

Both alts. have bad brushes or an open field coil.

The light grounds thru the brushes and field coil so both need to be good for the light to work.

Full battery voltage at both pins w/engine stopped shows there is no circuit thru the field coil to ground.

Pin from the lamp should be about 3.7 volts,IIRC

Put a jumper cable between the alt case and battery negative as another test for a poor ground.

Not too surprised if both of them are bad. I wasn't too sure how those lights were grounded, but if it is through the brushes then that makes sense. The one on the car definitely has something bad inside it. After removing it, I noticed a rattling noise when shaking it. The spare replacement is pretty crusty so I'm assuming corrosion may have killed something in that one as well. I will report back after the new maxima alt shows up and is installed. 

Thanks for the help fellas!

Got the maxima alt installed! Sweet upgrade. Too bad i didn't actually need one. The charge fuse was showing good when I checked with my power probe, but I didn't actually pull it out to look at it. Dumb mistake, but it did look good until I checked it with the dvom and found it was burnt. Thanks again for the help guys. 

A nice reminder to keep it simple!

"Bugger!"

At least there was a positive in it!  Upgrades are always good! 

Cheers

Bennie