2001 ford explorer xls new battery new mfs will not turn over
...yes, well the battery GROUND is connected to a point on your chassis...wire brush that lug and the point where it attaches to the frame....also the 1/0 cable that runs to the motor block (near the alternator)...if this isn't in place your vehicle is gonna struggle for the cold cranking amps~
Check the small wire going to the starter solenoid. These are bad about corroding or falling off. If you have good connections at the battery and this wire is ok check starter relay or replace the starter.