Newer year parts added to older model car and wiring is somewhat different

98 monte z34 tensioner went bad, gf ran across
monte at junk yard a few years newer, got the
tensioner and alternater from 02 cause the
tensioner had mount different than for 98 z34 so
had to use the alternater from 02 monte due to the
mounts.  98 z34 had one wire plug to alternater but
for 02 monte it should be a 4 plug wire.  Her volts
light always stays on.  So how and where if i by the
right 4 plug for the 02 alternater do i wire the other
3 wires.  If anybody can follow what im trying to
say and can guide me in the right direction i d
appreciate it.  Thanks much