i need to know how to wire my 3 wire alternator in my 87 iroc,

right now the wire on the back post goes to the battery, the fat wire from the clip is jumpered to the post on the back and the little wire goes to a 12v ign. source

my battery is not charging up from when its dead

i hooked a votmeter to the battery when it was running and it was showing 14v,

what should i do?

the wire on the back post goes to the battery, Yep
the fat wire from the clip is jumpered to the post on the back,
There will be a terminal marked with a "F" that is the feed to the feilds, this goes here
The other wire is for gen light etc