Help!!! External voltage regulator??? Options

[pengwen]

I have a 94 celi. recently i'm driving down the road and my battery light comes on and I lose my power steering. ok so classic alternator symptoms right? wrong alternator test fine. battery test bad. so all i can figure is there is an external voltage regulator. the alternator states that it has one built in.
a) can a voltage regulator in an alternator be bad but the whole thing still test ok?
b) do celica's have a separate regulator? if so where is it?!!
c) any other ideas what it might be?

any help would be greatly appreciated.
i'm driving a big hoopity van cause my celi's broke and the gas is killing me!!!