New Battery and Alternator, and battery won't charge - 2002 S10

[psypgmr]

I have a 2002 S10 with 2.2 4-cyl. I have replaced the battery and alternator, and the new alternator will not charge the battery. What do I need to check? The cables and ground are clean, and I get the full 12 volts when not running; but get no charging output when running.

[00Silverado4x4]

I'd take the alternator back to wherever you got it and have it tested. If it fails to charge they should be getting you a new one.