What would keep drawing down the battery? on 1996 Mercury Sable

We have replaced the battery,mega fuse and the constant control relay module. We want to remove the alternator to have it tested. Tests so far show no problems however the car keeps dying and the battery light keeps coming on and the battery keeps drawing down.

Asked by for the 1996 Mercury Sable
If the battery light keeps coming on, there is an issue in the charging system.
What might that issue be? Where should we look?
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1 more answer , 3 more comments
More than likely the alternator is the cause. If this is a problem when the vehicle is not running, you have a parasitic draw. Something is staying on when the vehicle is shut off.
We have had the alternator tested and it tests ok. We are trying to remove it from the vehicle to have it checked,however can not figure out how to loosen the tensioner on the serpentine belt. Can you help? We can not figure out what is "on" when the car is "off" any ideas there?
No I don't know....usually the hood light is a culprit. It stays on when the hood is will know if you open the hood and the plastic cover is almost melting hot. Otherwise, it could be almost anything even a loose wire arcing to a metal surface. here is the tensioner location: Just scroll down.
Thanks for all the help!!