Hello Hummer Fam. Hope all is well. I need some guidance from the gurus on here plz. So I have a 2007 hummer h3 base model. Just recently changed the alternator and starter along with a brand new battery. 3 days later I find out my alternator isn't charging my battery. It was the first 2 days but on the third day my h3 died in traffic which is embarrassing af. I've tested the alternator and I'm getting 12.6 but when I test the battery w h3 on the voltage is dropping and pretty quickly at that. Ive checked the plug because I did install a new 2 pin plug wire due to the old one being messed up. Any help would be greatly appreciated.


I would like to add that about 3 or 4 months ago I did add a decent size audio system to my h3 which is why the original alternator went out and needed to be changed. I will be upgrading to a high output alternator when i can afford one because i dont have a spare $500 rn but this new alternator should be plenty fine until I can afford a high out put alternator.

 

I have purchased a brand new alternator for a vehicle only to have it go bad a soon as you start the vehicle with the belt on. Happened twice over the years. Just because it is new is no guaranty it is going to work correctly. 12.6V at the alternator is pretty low, should basically be over 13V almost all the time, 14V+ when you first start it.

Since you did wiring, I would suggest you retrace your steps for any issues. I also have to ask, are you still trying to use the Crappy Azzed OEM Battery Terminal Connectors? If so, they have to go. Hack them off and replace with a quality aftermarket set like Stingers or your favorite brand. #1 mod to be done to every H3/H3T.

Perhaps you amp load is overtaxing stock alternator output?

 

$500.00 for an H3 alternator?

AMAZON has HIGH OUTPUT alternators for the H3 for $130.00

 

And when you have to do all the work again because that cheap crap fails, the good feeling of saving a buck will be long long gone. The Alternator swap on the I5s is a PITA, lot's of work.

 

Doc Olds-I'm lucky-I've had an AMAZON 'alternator'- on my H3 for 4 years... Still working like a champ
Most all the alternators that you buy today, are either made in Mexico or China,

 

"Long after the taste of cheap wears off, your decidedly left with a dissatisfying taste in your mouth".
I heard that when I was a much, much younger man lol!
It took years to finally absorb the wisdom in this profoundly simple, yet wise statement.
When I did my H3 alt I purchased a GM / ACDelco. If not that then I go to VatoZone and get the Gold lifetime warranty. I'd say guarantee but that's how often your guaranteed to change it lol.
I'm on my 2nd or 3rd lifetime water pump already. So, your guaranteed to keep replacing it. Last one made 5-8k miles. jmho

 

High Output Alternators are hard to come by for the I5 H3/H3T Colly/Canyons. The usual culprits like DC Power, PowerMaster, PowerBastards, Mechman and JS Alternators do not have them jumping off their websites, but might do a custom order if asked?

I have my eyes on a Mechman for the Alpha (Made in the USA) at some point.

I do see one from GP Car Audio (Made in the USA) for the 3.7L, and Alterstart on ebay has a couple, but they are just a nominal bump above OEM output.

 

Your new alternator is bad - 12.6V is not enough to charge your battery. My Alpha will charge at 15.1V right after starting the engine and the typical float voltage once the battery is fully charged is between 12.8V-13.1V. Your fully charged battery should have a resting voltage of 12.8V.

 

My '07 original factory assembly line installed alternator still works perfect!
12.6v resting
11.4v cranking
15.1v after startup
13.6v after idling 4 minutes
12.8v after idling 10 minutes

 

[size=16px]Thank all of you guys for the words of wisdom, and advice. FINALLY for once in my 35 years of existence I've gotten lucky when it comes to something being broken on my own person vehicle. I'm so unlucky that I don't even know where to start when something breaks lol anyone else's car I'll start with the cheapest s*** first and work my way outwards but with my vehicles it's been the complete opposite, it's always the most expensive s**t first for my vehicles. I cant believe It was just the stupid dumba** 125a Mega Fuse. This was going on for almost 3 weeks before I was so tired of having to put the trickle charger on my truck every single time I used it. I charged my H3 more then I've charged my phone these 2 weeks. No bs. So as stated after first looking at it when the problems first occurred I was completely stumped. I consider myself pretty mechanically handy but even my real mechanic buddies didn't really know what to say besides the usual check your fuses and I did but there's no way of telling a Mega Fuse is bad or not. It can be corroded but by looking it's impossible to tell good or bad. I'm sure it can be tested but idk how to do that and I probably wouldn't of looked because I would of never guessed I can get so lucky. Lol. I was at O'Reilly's for something and figured I'd get a Mega Fuse for like $6. I figured wth I'm from and live in Vegas let's gamble and I freakin hit it big finally boys 🤣 🤣 🤣 sorry for such the long response I just felt that needed to be said to understand the significance of my bad luck with my own personal vehicles. Not that anyone cares lol[/size]