1999 mercury cougar wont start

What engine ? 2.0l 2.5l 4cylinder 2.5 l v-6 wrong parts or needs to be shimmed . Motorcraft parts or aftermarket ?

You have fusible links supply power

right below fuse 15 in the battery junction box/ fuse box under the hood.

chekc your fusable lnks that go to the starter solenoid and battery even though they may not look phsycally broken or burnt most times they seperate internally so check voltage at both ends of the fuse links

Change the coolant sensor near the thermostat housing. Good luck!

V6 ? 4CYL? Have you verified SPARK? Did anyone check the "fuel pump inertia switch?" Its in the right front kick panel. If it was a "Anti-theft Issue" the light would be on or flashing.

Yout whole fuse box might be blown. I had to replace mine on a 2000 Cougar.

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!!

Two things could be one the ground on the starter itself bad, aslo check the small wire that pushes on the starter. The most likley reason is the starter has failed if the battery tests ok.

1) Look for external ford starter solenoid or,2) Try on neutral, the parking transmission switch, 3) Look for fuse or a Relay on engine compartment