Charging System not charging...

[Gabeasorus]

It seems that this is a fairly common problem seeing as how there are many threads dealing with this exact issue so heres my specific problem...
My alternator is not charging the battery - at all.
Heres what I've tried so far:
Replaced battery (first sign of trouble) Duralast 75-DLG
Replaced starter (in the Autozone parking lot )
Replaced alternator Duralast DL7273 - 3 wire red/brown (clip) and red (nut)
Replaced battery leads and cleaned all grounds
Tested alternator on bench - good
Tested alternator in truck - not so good
Tested battery in the truck - 12.39 volts
Put a meter to the 3 fuseable links in the charging system (battery disconnected completely) - all good
Put a meter to the brown wire that clips into the alternator (battery connected with key off) - good
and to he brown wire with key in on position (but not running) grounded to battery I get 12.39 volts

So what gives?
From what I've come to understand,(according to the official GM shop manual for my exact model) this brown wire actually ends up at the key switch (not the instrument panel as the Haynes manual depicts) and brings resisted voltage back to the alternator as to keep the alternator charging. (Thanks Dad) I don't seem to be getting resistance from this wire. Its exactly the same as the battery. So I think the alternator is not "engaging" because it doesn't think the battery is low?

Anybody?