So, the regulator circuit is in the ECU then. That complicates things.
So, the regulator circuit is in the ECU then. That complicates things.
In reply to Vigo :
Smacked it. Voltage jumped up to 14. I'm pretty sure that rules out fancy electrical stuff.
Doesn't anyone make an OE or OE+ type alternator so I don't have to play reman-roulette? It's a 5.3 LS, they must sell 10k alternators a day for these things.
If you're willing to pull the alternator apart, you can probably get new brushes and just pop yours open and fix it up. Or have a local alternator shop do it if you can find one.
Most newer alternators have a regulator and brush assembly combined and it is externally serviceable.
Give it a look see and if the bearings are quiet replace the brush assy and call it rebuilt?
Those look like they're dirt cheap as well; under $20.
In reply to mazdeuce - Seth :
Newer gm alternator are ecu controlled
Alfaromeoguy said:In reply to mazdeuce - Seth :
Newer gm alternator are ecu controlled
Can the ECU turn it off? I know there is a sort of dual mode where it will set voltage at either 14.4 or 12.5 volts depending on running mode to save fuel, but will the system default to one of those modes or can it just be off?
If you smacked it and the voltage went up that's a dead giveaway of worn out brushes. That also explains how it worked for the parts guy but not for you. This is pretty much best case scenario because those alternators are readily available and very simple to r&r (twice even!). Almost certainly cheaper than any time you would spend chasing an admittedly more interesting wire problem. 
In reply to mazdeuce - Seth don't know,sorry, ran across this during my ecotec to Alfa Romeo spider conversion.
mazdeuce - Seth said:Kid at O'Reillys threw it on the tester and said it tested good. Threw it back on the truck and it's still sub 12V.
Come on man. You know better. I went through three starters that tested fine at the store but wouldn’t spin under load. Brand new out of box.
Did anyone have a link to the brushes/regulator for this? I'm having a little trouble finding them online.
And some more info. Hope this helps you reenergize.
Talked with Mrs. Deuce. The truck still has enough very long/cross country trips planned that she wanted me to spend the few extra dollars, put a factory new ACDelco alternator and two new belts on and call it good. This is supposed to be the vehicle that rescues my other crap cars, so it seemed prudent. I'm likely to try and rehab the old alternator just for fun as well.
mazdeuce - Seth said:Kid at O'Reillys threw it on the tester and said it tested good. Threw it back on the truck and it's still sub 12V.
I went through this once with my Ranger. Turned out the positive battery cable had internal corrosion. I changed that cable and all became well in Whoville.
Part 2 - if it the alternator is bad try to find a local shop that can rebuild it. (If you can do with out the vehicle for a day).
Usually a lot cheaper than a Stealership. A little cheaper from a rebuilt at a parts house.
mazdeuce - Seth said:Talked with Mrs. Deuce. The truck still has enough very long/cross country trips planned that she wanted me to spend the few extra dollars, put a factory new ACDelco alternator and two new belts on and call it good. This is supposed to be the vehicle that rescues my other crap cars, so it seemed prudent. I'm likely to try and rehab the old alternator just for fun as well.
Mrs. Deuce is right.
If the alternator reads lower than the battery, it's almost always the alternator.
New alternator on. Fired it up and the truck is happy as a clam. I'll change both belts when I do an oil change because the AC belt it easier to do from the bottom with the splash shield removed.
Thanks for the help everyone.
Check health of AC belt tensioner when you do the belt. I’ve had several explode/seize and done them for a few people. With miles on the truck it might be cheap PM, unless it’s just up here in the land of salt death.
If you want the alternator rebuilt by a real shop send it up here and i’ll have it done for you, we have an amazing place in the heart of the hood on the west side of cleveland that i take all my old stuff to for rebuilding or conversion to 12v instead of 6.
Not that im disagreeing with checking belt tensioners but the ac belt on this one might be a stretch belt. I know they were by 2011, but i dont remember how far back that goes.
In reply to Vigo :
The newest one i’ve done was a 2007, but was a van and they held over lots of old stuff on vans(07 vans still were 24x crank sensor gen3 stuff)
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