everything is new, but still won't charge...

[71wongbed]

So, I have had this problem for a little while and thought I had fixed it, but I was wrong.
My battery is not being charged by my alternator. I have replaced everything: alternator, ext. voltage regulator, battery AND re-wired the sucker, but it still won't charge. I have eliminated shorts (pulled NEG off battery and from cable to post reads 0V). I had Autozone test the brand new alternator 4 times and it passed, and I disconnected the POS off the back and read 1.5-2+V output, depending on engine speed. Like I said, I built a new harness- the only difference from my harness and the one in the beautiful PDF that floats around is that there is no fusible link between the POS on the battery and the red wire that feeds to the alt, reg, dash so on. Is the fusible link going to keep it from charging?
While running, I test the red on the back of the alt and it just gives me the same reading as the battery. No more, just usually 12.4 or less, depending on the charge of the battery. This is honestly killing.
I know it is hard to help troubleshoot over the net, but any suggestions outside of replacing the truck will help immensly (I plan to call Car Talk as my next step so if anyone could offer any advice that would keep me from that shame...)
Thanks!

Reuben
71 C-20, 350/350, nothin' special