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The alternator on the left is not isolated ground and is not original to the truck.

The front battery is dead. You say above that you are taking the battery reading at the posts. I'm assuming you mean both posts because you say with "the cables" (plural) unhooked it reads normal. If the cables were putting a large enough load on the battery to make the voltage zero, that would...

Those companies are buying from a common importer so they would all have the same thing. WAI's is probably the biggest importer, and their website has the same alternator as in the link in the first post. The only difference was the color of the insulators which could have been the picture. That...

12.35 volts per battery is not topped off, it's a 60~70% charge. Not keeping the batteries fully charged will lead to premature battery failure.

Battery voltage is 12.7 for a fully charged 12 volt battery. X2 for 24 volt system or 25.4 for a 24 volt battery pack. Either you are measuring wrong or the alternator isn't working.

Is there a manufacturer name on the box or paper work?

Search "21si alternator" on ebay. Several come up around $130 with free delivery.

He's talking about the driver's side alternator. That ground can be to the engine block since you can run a non-isolated ground alternator on the driver's side. I do wonder where the factory ground wire went though.

I completely understand 74M35A2. Like you, I worked in the rotating electric field for many years. I've done or had my tech do many durability/destructive tests on different new alternator components. I never offered complete units because of the reasons you mention. The regulator is not going...

Actually, that is not true. In fact, I can't think of any 12 volt regulator set point that is more than about 14.8. A 24 volt alternator is simply double that or a little less. I have a dual voltage 30SI in my M915A1 and it is 14 volts on the 12 volt side and 28 volts on the 24 volt side...

Over 32 volts is a little high. I would expect 29.5 to about 30 max for a 24 volt system. Is that a 32 volt alternator?

Alternator #2 is 14.8 which is the regulator set point so it's ok. Alternator #1 is 13.8 and that is low. If the battery is ok and just discharged it should eventually come up to about 14.8. If it doesn't come up to 14.8 or within a couple of tenth's of a volt about 5 minutes after starting the...

When I picked up my M373, the brakes were inop. But considering my M915 weights twice what the trailer does and it has very good modern air brakes, I was not concerned. I could not tell the trailer was there on the way home. An M129 is a tall heavy trailer and probably weighs more than your tow...

Plus 2. I start the truck in the morning and it runs until I stop for the night. It was two days home with my M929. I started it exactly two times to get home. The third time I went to start it after getting home, the starter had crapped out. It would have sucked to try and find or repair a...

In your other thread you said you checked both alternators after a 40 mile drive and had good voltages. Why are you replacing the alternator? Are you talking about two trucks?

We like pictures.

What were the good voltages?

Why don't you try using that meter to check the battery voltage at each battery while the engine is running instead of looking at the idiot lights? The battery voltage should be over 14 with the engine running unless it is dead. Alternator #2 has nothing to do with alternator #1, which you say...

Are you sure the alternator works? The battery shouldn't be dead after you have been driving the vehicle. I can't tell what scale your meter is on but assuming it's showing 830mA load, that would take a day or two to kill the battery.

I'm 150 lbs and I grab the handle and put a foot (or two) on the bumper and pull.