2001 mercury mountaineer starts fine but sometimes won't start at all

SOURCE: 2001 Mercury Mountaineer won't start

Have a load test done on the battery. If it checks out good, take a voltmeter to the battery and have an assistant rotate the engine. If you see more than a 2 volt drop when the car is being started, the starter is heading south.

SOURCE: 2001 Mercury Mountaineer keeps blowing the PCM power diode (fuse #19)

Check all of the battery terminals and cables and check the wires on the starter/selonoid, start from the battery and follow the cable out and check all conections , clean and tighten them and if it still does it the starter/selonoid is bad and needs replacement...

SOURCE: ignition

Sounds like the battery is dead, you have just enough power to have the lights come on, but no cranking of the starter. Try putting the battery on a trickle charger, or hook up jumper cables to another car which is running. Let it run with the jumper cables connected for two mintues before you try and start your car.

SOURCE: My mercury cougar won't start, all lights are ok

Take another look at the battery, clean the posts and the terminal ends. Charge the battery, or jumpstart from another vehicle, and allow it to run for 5 to 10 minutes. Shut the vehicle off and see if it will start again. If not you will most likely need to replace the battery.

SOURCE: Mercury cougar wont start

My first suspicion is the battery connections may be lose and also the battery may now be run down. If you take the terminal connections off and clean them and the terminal posts so that they are shiny clean and charge the battery you can try again. If the car starts, that was the problem. If it doesn't, then look for the starter solenoid and lose connections there and also look toward the starter next. A tech with a volt meter can run independent checks and narrow it down further but having good connections and a charged battery are necessary to get started with the other tests.