I'm not sure if it matters so much why the alternators are failing, when the bell curve of in truck solutions that would help prevent alternator failures is relatively narrow, and ultimately boils down to wiring.

Whether the alternator diodes are shorting or blowing, or whether the entire alternator is overheating, or whether the voltage regulator chip is sizzling... no matter what ails the string of new alternators being replaced every 7 months, if the truck itself is at fault, almost all of the possible solutions to resolve the root cause of the problem will in essence boil down to wiring. So it makes sense to examine all the charge circuit wiring, regardless.

If NAPA branded alternators (made in China or Mexico, depending on which model) are simply POS, then there is nothing we can do about that other than change brands/sources of alternators. But there is a valid argument for sticking with NAPA, in order to get every dollar of free replacement warranty already paid for with the price of the initial alternator. And regardless of whether or not the inconvenience of swapping alternators every year becomes so irritating that the warranty is abandoned for a more reliable brand, if the root cause of the alternator failure is the truck wiring, then a new USA made alternator wound from virgin copper mined from Montana may last longer, but still won't fix the problem. So might as well look at the truck wiring anyway, irrespective of why the alternators failed.

 

ya Y2K..what Denny said...thank you for the time, effort and knowledge you bring to the table

 

I think after I check the wiring this Saturday, I'll change from the pos NAPA free replacements to an OEM for the sake of construction.

I thank you for your time and expertise!

 

NAPA usually makes good parts, much better than oreilly or autozone .... I still think your batteries are weak, or your alternator wiring is corroded/faulty

 

I agree that something else is going on.

I'm not sure what your interest or budget is but I got my alternators from here and have been very happy with them: https://alternatorparts.com/

 

https://www.knowyourparts.com/techni...ators-replace/

 

Clean battery connections doesn't give the battery cables a clean bill of health. Corrosion is insidious, and can wick inside the cable jacketing, causing resistance. A fusible link may have separated, leaving the other with twice the load it is rated for, in a wire diameter that is 4 times smaller... which can cause resistance. The by product of resistance is heat. When the alternator output is wasted through heat, rather than directed to recharging the batteries, then the batteries get weakened... rendering even new batteries, or batteries that are only 2 years old, crippled in their performance, which further taxes the alternator. The weaker alternator, crippled now by highly resistant wiring, and anemic batteries, can never truly catch up to fully recharging the batteries, so the batteries never get completely charged, which further weakens the batteries, which further taxes the alternator. Endless loop, until you take battery CHARGING in your own hands.

First thing, charge the batteries OFFLINE from the truck's electrical system, using a plug in the wall charger, without relying on the alternator to "recharge" the batteries. The alternator cannot and should not be expected to charge dead batteries, unless you have a really bad a** mama jama alternator that can put out over 100 amps at idle. By comparison, the oem alternator only puts out 50 amps at idle. But even with a big honkin alternator, best practices dictate that the batteries should be recharged on shore power whenever an alternator is replaced, because if you are replacing an alternator, then something was wrong. It wasn't doing its' job.

Whether the fault was the alternator, or the truck in the form of resistance in the wiring in between the alternator and the batteries, it can be safely assumed that by the time the light came on the dash, the batteries were supplying more the truck's electrical power than the alternator. It wasn't even giving you 50 amps. The red light on the dash said that the voltage from the batteries is about 1.5 volts greater than the voltage from the alternator. To charge a battery back up to 12.7 volts, just the opposite has to happen. The voltage from the alternator has to be at least 1.5 volts greater than that of the batteries. Hence charging voltage is between 13.9 volts to 14.4 volts, temperature compensation and voltage reading location depending. Picking a median between 13.9 and 14.4, we find that 14.2 charging volts minus 1.5 voltage difference equals 12.7 target volts for a fully charged battery.

Hence, by the time a problem is discovered with an alternator, there is ALWAYS a problem with the batteries at that moment, regardless of how new the batteries are. In that moment of discovery, the batteries are not fully charged. If you swap in a new alternator without first charging the batteries, then right off the bat the new alternator is operating under a handicap, because it's principal role is to MAINTAIN battery charge, not necessarily RESTORE battery charge. Use a good 25 amp battery charger to restore the batteries first, before installing another alternator.

With the batteries fully charged, THEN you can load test the batteries to make sure they haven't already been ruined from previous failed alternators never being able to catch up. Several ways to load test batteries, including a cheap carbon pile from Harbor Freight, or a high quality calibrated ribbon resistor load tester from Snap On, Sun Tech, Bear Equipment, or the like, or one of the new electronic capacitance testers from Midtronics or equivalent. I use a traditional professional tester, somewhat vintage today, but that once was a $4,000 state of the art battery analyzer. Napa should have something similar for internal use at their store, to help them render decisions on battery warranties. It sounds like you plan to ask them to load test your batteries (after you charge the snot out of them with shore power).





If the otherwise fully charged batteries fail the load test, then you have to replace the batteries, otherwise you will continue to replace alternators, and then still have to replace the batteries. But before dropping in the new batteries, go over every single connection in the charging, starting, glow plug, and GROUND cables. That is essentially what every single respondent to this thread has been saying all along, using different words, maybe, but ultimately the chorus here is singing the same tune.

After all that, if you want to get fancy, then add additional cables so that the batteries can get directly charged by the alternator without resistance. The additional cables provide parallel paths that offer fail safe redundancy should corrosion develop in a cable or connection. With parallel redundancy, corrosion hidden under a bolt or inside a wire jacket of an OEM cable no longer becomes a show stopper in keeping the batteries charged.

The batteries in my photos above are over 10 years old, btw, and still kick the 7.3L over on a cold morning like Adam Vinatieri kicks a football in the clutch. I charged these batteries using a smart charger on shore power before installing new alternators, and haven't touched them since (no trickle charging, no tenders, no cords). I start the truck a minimum of 10 times a day, and most of my trips in the truck these days are less than 1/4 mile. Not much charging time, and not much freeway time. But the alternator I installed can produce 100 amps of current at only 670 engine rpm, and there is a lot of copper and grounding to pipe that current directly to the batteries after they did their duty running the glow plugs and starting the truck.

Batteries can be considered dead at 12 volts, and fully charged at 12.65 volts after the surface charge from fresh charging as been depleted or zapped off.

 

Great points and great summation!

You've definitely given me a weekend worth of work to do and I greatly appreciate your time and expertise!

Many thanks !!!

 

Those days are over, and but true you will find more made in usa parts at Autozone than any other parts store these days. Napa has been playing catch up over the last 10 years and quality is gone. I used to buy all my heavy class 8 truck parts from napa but they switched all their brake drums and linings to made in India so now I just get them directly from Peterbilt. I remember when Echlin was high quality and NAPA ruined that.

 

If you happen to live in my neck of the woods I have one of those fancy $3k+ Midtronics analyzers that'll test the batteries and the charging system. I don't know for sure that it would 'see' a faulty connection, but maybe.

 

I went the parts store route on my starter saga (NAPA in this case). While I totally agree with making sure all your wiring is good. I would not be surprised is the alternators are garbage. I have a neighbor with a 2000 7.3 and his OEM alt went 16 years and then went through 2 alts in 6 months until he got a good one. Very similar story on my starter(s). The problem is that replacement parts are not giving OEM service life. Now, when you have an 18 year old vehicle, even OEM parts are mostly suspect as they are procured from the limited sources that everyone else gets their parts from.
The trick is to find exceptions to these distribution networks:
*Find companies in the replacement parts business that are also in the business of supplying OEM's. Harder to find because end user business is secondary. The hub place in Michigan comes to mind here. Also Alliant to a certain degree.
*Local rebuild shops. Got to find one that doesn't use Chinese rebuild kits though - hard to do.

I personally think that Alliant holds a lot of promise for guys like us; lots of it actually manufactured in the US. They work closely with suppliers to the OEM's. They are aware that there is a quality problem in replacement parts. Don't take my recommendation as I haven't used them for anything yet, but the next time I need something, I will try Alliant.

 

harbor freight should have a cheap battery load tester, you could test the batteries in 2 minutes .....

 

My batt light came on today so I came searching for information and this is the 2nd thread I found where numerous alternators were replaced one after another.
In my poking around I discovered simply unplugging and reconnecting the two wire connector got the alt charging again.
I'm not saying this is a fix, but think it is worthwhile for the OP to try versus replacing another alt and having same problem.
​​
​​​​
That said I'm curious as to how all this works, As said by someone above you need to understand the problem to cure it...
1. What causes the in dash batt light to illuminate?
My voltages tested between 12.47 - 12.50 at both batteries, charge plug, and both terminals of the alt connector while removed.
After testing the connector and plugging it back in voltage at batteries jumped to high 13's
2. What are these two wires for?
3. Where does the alt charge cable go after it disappears into valley?

 

I'm still trying to figure this all out myself!!!

 

I too had a spell where alternators would fail after 6 months or less. I bought mine from a local rebuild shop. The first one I bought from them went for 5 years but subsequent ones kept failing to the point where I was on a first name basis with the shop. I also found the trick where unplugging the connector and plugging it in again got the alternator charging again. The literature I found on what that plug is for is conflicting. Some of it says it's the signal from the PCM to tell the alternator when to start charging after engine start. Others say the voltage regulator (that's the part in the alternature that holds the brushes and has the hole for the plug) determines the after-start delay of the start of charging. I also found that wedging two quarters (hey it's the new 50-cent mod) between the frame of the alternator and the plug would get the alternator charging again.

I eventually ended up ordering heavy duty parts from National Quickstart and rebuilding the alternator myself. I also added their external rectifier. That has only been running a few months so we'll see if that fixed my issues.