1997 rodeo Alternator

Hi all,
a freind and i are working on his 1997 rodeo with the 2.6 4cyl.
his alternator stopped charging yesterday, and we replaced it with a new one and it still was not charging. a mechanic at a local shop said to look at my wiring schematic for the wire that goes to the ecu which is labeled gen gain control. he said to hook this wire to ground and see if
it would charge at all, and if it did the computer is bad. so we tried this and it just barely charges putting out 11 to 12 volts. it will not let the battery get low enough to stall the engine but if you run any accessories, you wont have enough juice to restart it.

my question is what does this generator gain control do and can we possibly wire this some other way to make this thing charge so he can at least trust it to drive back and fourth to work next week
thanks for your help,
Kyle

according to stuff ive read elswhere this wire is supposed to trigger the voltage regulator anyone know what it sends to the reg to trigger it??????????? please heellpp as we reeeaaallly need to get this fixed!!!!!!!!!!!!!!