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?

[mckpaul]

As for a couple of added comments from Gabe's dad (that would be me)...

From what I can tell, that brown wire from Term. #1 on the two wire connector on the alternator eventually turns into a 'resistive' wire on it's way back to a 'run' terminal on the keyswitch.

As I understand it, on trucks with an Alt light, that brown wire gets positive voltage thru an 'ALT' bulb on the dash, so the bulb acts as a resistor in the circuit. But on the trucks that have volt meters, the volt meter circuit is a whole different circuit not even related to the brown wire on the alternator. The brown wire still has to go to a switched circuit but since there's no bulb in the circuit, GM made a section of the wire a 'resistance' wire. From what I've read, the alternator uses that brown wire as a trigger to turn on.

As Gabe mentioned, we've checked all the fusible links in the system with an ohm meter and they all check good. The alternator checks good in the store on the test bench, but in the vehicle the charge isn't making it back to the battery. If the brown wire on the two wire plug is what tells the alternator to 'turn on', it doesn't appear to be making it happen. As Gabe mentioned, the brown wire does get voltage when the key is turned to the run position.

I'm scratching my head on this one. Hoping someone has had a similar problem.