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I recently bought a 99.5 AEG 2.0 Auto that was not running due to a bad Head Gasket. Once I got it running noticed it was not charging the brand new battery. I had the alt rebuilt and bench tested when done and everything checked out. Once installed it is putting out 12.3V when idling. I replaced cables and cleaned grounds under battery and same issues. Any ideas? I don't know where to go from here. Thanks for the help.
 

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This may sound stupid, but the small plug is securely connected, right?

Does the battery light on the dash illuminate to indicate that it's not charging? Check then fuses, my wiring diagram says it's fuse #11, 5-amp fuse. Also check the big 110A fuse near the battery.
 

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Discussion Starter #3
Small wire is tight I triple checked that. I checked fuse 11 and seems good. Is the 110a fuse just a metal fuse on top of battery where the wire runs to? It isnt burned at all and seems fine. I have also noticed that the coolant fans are not running. I am not sure if its related or not. Thanks
 

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Yes it comes on occasionally. That is what alerted me that there was a problem. It does not stay on constantly.
 

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Verify the integrity/connections of the big wire between the alternator and battery. Also try to verify the accuracy of the light...is the alternator actually charging while the light is off?
 

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Discussion Starter #8
thanks for your help i really appreciate it.
I replaced the cable between alt and fuse box and cable from fuse to battery and verified connections
and no change
Only puts out 12.3ish volts while idling measured at both the battery and alt and when i turn car off battery voltage rises
 

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on top of starter is a 4 pin conncter. it is actually the alt. harness which includes the signal wire to the alt. and a/c compressor. its worth checking, sometimes the torque(twist) of the engine can stretch the harness and cause an open. off top of my head possible connection from cluster to alt. under driver side plenum connector(under wiper transmission). not sure on your car but have seen v6 passat with loose connecter doing intermitant charging. also, a bad ground cable can do some funny stuff, under battery tray and engine. voltage drop test is best in that situation IMO. cheers bern
edit, i expect 14.1-13.9 volts at idle.
 

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First of all, stop replacing parts unnecessarily. I said verify, like check it with an ohmmeter and make sure the connections are good and tight. You didn't have to replace that wire, or the fuse box :p

I guess you're getting 12.x volts with the battery light off? Still not 100% clear on that.

If you're only getting 12.x volts at idle, even with the battery light off, it's time to check the signal circuit. You already verified that the fuse is good, you've gotta check the wire from that fuse through the cluster, and back to the alternator. It may run past the starter as jettatech suggests, I don't know off the top of my head. If I have some time when I get to work I'll pull the wiring diagram.
 
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