Turn key nothing, but battery still works - 2001 Ford Taurus

battery is dead, or lugs rusty
if head lamps fail even not using the key
then the battery is dead.
jump start it if stranded or call autoclub for a boost.
held lamp , bright even key in hand not used.
they work at any time even key lost ,by laws. USA)

If the battery is dead, the first thing to do is get your battery charger out and charge the batteries up. Nothing works without battery power.

when you lock it up does the alarm activate you say this problem only started after changing battery sounds like its the mobiliser lock and open car from inside with key in ignition hope this helps

If you have a second key, try that one. Sometimes 1 key will unlock, 1 key will start. If not it would be the anti theft or security system disabling the ignition module. Which is why it won't even try to turn over.

Check the battery cables again. Both positive and negative. Check the other ends of them also. Could be a loose connection or bad contact.

If you are sure the battery is charged and nothing happens when you turn the key you have a poor wiring connection somewhere or possibly an poor connection internal to the battery. First, turn on the headlights, then try to start the car. If the headlights go dim when you do that, you have a bad connection. If they stay bright, you are not completing the starting circuit. The most likely cause is a bad battery post connection. Remove the terminals and clean them to shiny metal then replace and try again. If that does not work try it again with a new battery.

You need a wiring diagram to start your testing

Guessing won't get it,waste of time

It is old enough to be a fusible link corroded

Some things work some don't,starting circuit
included if not a bad starter & separate problem

You can solve almost looking at a wiring diagram
as you know what deosn't work

Check the tremianls on the battery. also follow your ground cable to where it is attached to the frame, motor or body. if the cables are in good shape, cut off the old terminals and replace them with new ones from the parts store. They are only a couple of dollars each.

Check battery full charge, battery terminals are clean, cables aren't cracked, broken or corroded and alternator first.

Which your having replaced your starter with new already. If you're still getting nothing it sounds like a bad ignition switch.

They wear normally and need to be replaced. But as a helpful hint don't place excess keys or weighty trinkets on your ignition keys.

They wear on the seating of the key in the ignition and often promote failure in the ignition from bearing the dangling weight.

What happens when you turn the key?... is there a clicking or clunking noise?... try tapping the starter and the solenoid that is attached to the starter and see if that helps. It may help if you have someone else turn the key while you tap on the starter and solenoid.