I have a 2000 explorer switch out engines now won't start, when I turn the key on all lights and instruments work fine but won't crank, checked battery volts which is 11.6, checked volts to starter with switch on and the volts is 6.3 but when I turn the switch off the volts is 11.6. I am lost could this be a bad relay. can anyone help me.

 

I don't know , but we'll try.
First of all , either the battery is low on charge or you have corrosion in the cables.
You must have 12 volts minimum to start.
Next question is , does the vehicle have a PATS (passive anti-theft system) ?

 

Yes it has a VATS, but do you happen to know why the voltage decrease when I trun the key on.

 

I had the battery charged at auto zone.

 

What is the no load voltage reading at the battery with nothing connected to it?
Where are you taking the reading at the starter where you get 6 volts?
What is the status of the indicator light for the alarm system when you turn the key on?
Have you double checked that you have all the ground wires connected ?
Battery voltage should not drop that much at the battery when you turn the key on if you have the test leads connected right at the battery. If it does , no matter how much you charge the battery , it is defective if the above steps and connections are correct. The alarm system will prevent starting and fuel pump operation if the wrong key is used.