Altenator Problem

[krappy]

I thought my altenator went out so I took it off got one from a friend who took it off his running KA and when i go to put it on i cranked it up with a battery booster... let it run for 5 minutes...came back took off the battery booster and the car just dies again.....any ideas? what else could be the problem?

[benefitx]

im the friend who he got the alternator from...the alternator is off of an SE S13 so its the 90a (IIRC) ....he has a kouki s14 so could that be a reason? because the alternator was pulled off a running KA which blew a rod through the block so i know the alternator is good because i never had problems with it..