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TrailblazerSS AWD
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Discussion Starter #1
So over the last few days I was working on my truck. Installed a new water pump. Dp hoses. And powder coated the alt bracket. Along with a brand new high output alternator.

Finally finished everythinf , get my truck back together and go to bleed the coolant, and notice my truck is acting all funny.

I was following the ss shootout way of bleeding the system. At the time I had my truck running with the heat on full blast. All of a sudden I notice my headlights flashing on and off rapidly. I look inside my truck at gauge cluster and it's lit up like a Christmas tree. Service abs. Service stabilatrack. Service tire monitor. Check engine light. All sorts of lights are all on. Plus I look at the volt gauge and it's dropping FAST!

I shut the truck off and inspect all my connections to make sure everything is tight. They all are. I try to start my truck again but it doesn't have enough juice to start. So I put my battery on the charger for awhile, then give it another go a little later. Truck starts, volt gauge goes up to 12v not the normal 14. And within about 10-15 seconds it dropped to 9. As the gauge was dropping more service lights started coming on the gauge cluster. Lights started dimming. Etc. So I shut it down again.

So Idk wtf is going on. I'm assuming it's the alternator not charging? But the alternator is brand new. I even swapped the alt out for my old stock one (which worked the day before just fine) and it still didn't work. Then I assumed it wasn't getting a good ground because of powder coat. So I sanded down the contact points even more. All the points where the bracket meets the motor. And where the bracket meets the alt. I checked the ground on the alternator after everything, and it is grounded. So it's not a bad ground.

Anyone have any ideas. The only thing I touched that had to do with anything electrical was the alternator. And I disconnected maf when I removed the intake. But everythinf was done after I disconnected the battery...
Alternator has a good ground, I checked it.
Checked the big monster fuse at fuse block. It's not.blown
What are the chances that both alternators decided to crap out at the same time? Not likely so I don't think it's a bad alt.

This has me going crazy. I can't figure it out. Any help is really really appreciated. What would be draining my battery this quick.
 

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Premium Member
TrailblazerSS AWD
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Discussion Starter #4
Some wire is loose or has a bad connection. I know u said you checked it but I'd bet money that something has a bad connection.
The only thing that could be loose would have to be the wire off the back of the alt, right?

You did put the right year ALt on it right....They are different. Stupid question....But plugs matched up right?
Yeah both 4 prong. Plugs match. I even threw my stock alternator in and checked the truck with that. Still had same problem.
 

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TT AWD TBSS Jeep
TT AWD SS Pwrd Jeep
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5,825 Posts
1. Ohm the prongs sticking out of the plug to further back in the harness. On my 06 the wires going to the alt where short and where kinda tight and one messed up right at the plug where the wires bend 90° and have too much tension. Make sure you both wiggle the wires while doing this and also bend them 90° while pulling harness taut to simulate being plugged in.

2. Did you test the voltage at the alt stud or just at the battery, could be a bad connection there too. (Much less likely)

3. Find which wire goes to the alternator that controls voltage from the ecm. Then google if it needs a ground or 12v to command max charging and apply whichever one it needs to do so. Only do for a short time while measuring voltage as it will most likely end up making 17v. When you test for voltage, do it at the stud at the back of the alt first, then at the batt to check for voltage drop.

G/L
 

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TrailblazerSS AWD
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Discussion Starter #6
So I brought my battery and alt to autozone to have them tested. The alternator passed no problem. The battery was charged 100%, but failed the load test. Said battery is shot.

So I bought a new battery. Put that in the truck. Started it up and it ram. Only got 12v on gauge. And after about 45 seconds got a warning light, battery isn't charging.

It just doesn't make sense to me. Brand new battery. Brand new alt. There one wire that runs from the freakin alt to the battery. And it's connected and in tact. I'm lost on this one.

Only other thing I csn think of is the little harness that plugs into the top of the alt. This wire goes into the engine harness. Is the alt controlled by the pcm. Is the pcm for some reason telling the alt not to charge or some shit?
 

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Premium Member
Trailblazer SS
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Alternator was brand new from the auto parts store?
Could just be 2 bad alternator shitting the bed at the same time.
I wouldn't trust parts sellers to test anything. They connect a machine and push the buttons it tells them too. I think their "testers" are weighted to fail batteries.

When they load tested the battery and alternator. Do you remember the voltage of the battery when loaded? And the alternator amperage output?
 

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Premium Member
Trailblazer SS
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Do you have a voltmeter? If so do a voltage drop test on both power and ground while the engine is running. This will verify grounds and no resistance between the 2 measured points.
 

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TrailblazerSS AWD
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Discussion Starter #10
Thanks everyone for all the input. Figured it out today since I finally had some time to work on it. And honestly feeling a little dumb lol.

Turned out to be a bad ground. (What an idiot I know) I checked the alt snd it was grounded. But I guess not grounded enough. What I did today was take jumper cables. I put on end on the alternator casing, the other end to the negative battery terminal. And it worked. Fired the truck up and it runs at 14ish volts now.
I just gotta figure out why it's not having a good enough ground now. I sanded everything down where the alt makes contact to the bracket. And where the bracket makes contact to the motor.
Think I gotta sand down the inside of the bolt holes, maybe some powder got in there that's blocking a ground
 

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Just a noob
TrailblazerSS
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6,206 Posts
Thanks everyone for all the input. Figured it out today since I finally had some time to work on it. And honestly feeling a little dumb lol.

Turned out to be a bad ground. (What an idiot I know) I checked the alt snd it was grounded. But I guess not grounded enough. What I did today was take jumper cables. I put on end on the alternator casing, the other end to the negative battery terminal. And it worked. Fired the truck up and it runs at 14ish volts now.
I just gotta figure out why it's not having a good enough ground now. I sanded everything down where the alt makes contact to the bracket. And where the bracket makes contact to the motor.
Think I gotta sand down the inside of the bolt holes, maybe some powder got in there that's blocking a ground
I told you that from the start.....:winner_first_h4h:
 
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