1999 Mercury Cougar wont turn over.

I've had similar problems with mine. Try checking the cables that run between your battery and your alternator to make sure you're getting enough feed between the two. If those are ok, have your alternator checked. I've had mine replaced 5 times since I bought the car new in 1999 and the car apparently doesn't act like most other vehicles when it's going out. If the test comes back ok, test it again. I recommend having the alternator tested at least 3 times before deciding that's not the issue. Also, I know it's a simple thing but clean your connector posts on the top of your battery to make sure you're getting a good connection. Figuring out that was the problem sometimes has saved alot of hours under the hood. Good luck!!