Altenator Question

[mx3_guy]

I recently removed the altenator from my 93 gs, and when i reinstalled it, I noticed an extra single wire on the same line as the altenator positive wire and plug. It appears to have been off for a long time. Its rusty and the clip is broken. Can anyone tell me where this wire connects, and what its purpose is??

[mzdspd]

its for a sensor located on the lower half of the block. i can't tell u the exact location right now cause im at school but the wire is just long enough to reach the sensor.

[mx3_guy]

could someone tell me exactly when it connects to the block, and what its purpose is... my check engine light is currently on, so could this be the cause of it??