Flat battery, neutral safety switch, starter realy poor battery connections.
Yes. Without sufficient charge, the starter will not have enough amperage to crank.
Usually, the engine flywheel. A solenoid in the starter moves the starter pinion shaft forward (or backward depending on how it is mounted to the engine) to engage the outside edge of the flywheel (which has teeth to match the pinion gear).
does the motor spin..ie..crank? if no possible locked up engine..try spinning it by hand..correct size socket on front crank bolt turning clockwise.. possible bad starter motor does the starter engage when the key is in the crank possition. if the motor does crank your looking at a fuel or ignition problem
if it bolts on the starter assembly you are probably talking about the starter solenoid. basically its what makes the starter engage. if its a sensor that just bolts near the starter it could be anything from a crank position sensor to a knock sensor.
The small purple wire on the "S" terminal of an older GM vehicle starter would lead to the ignition switch. With the key in the start (crank) position, the purple wire signals the starter solenoid to engage the starter.
Have an experienced mechanic listen to the starter as you engage it and crank the engine over. He can tell if the starter is to tight, to loose or just right. There is a process to measure the correct spacing between the starter drive and the flywheel. Not easily done by a non-mechanic.
That's insufficient information. In general, "crank over" means that the starter is not turning the engine when you put the keyswitch to the "start" position. The starter can fail to engage because of a failed starter, solenoid, keyswitch, neutral lockout switch, faulty battery, failed alternator or just about anything that would drain the battery.
Usually when a starter solenoid/relay switch is bad, you will hear only a click and the starter will not spin (crank).
the starter solenoid is on the starter the starter relay is mounted on the drivers side of the top front main support in font of the battery
Replace the starter
Possibly if the starter solenoid contacts are weakened as this will cause them to reconnect long enough to start the vehicle or the plunger is seized in the wrong position. Once you start tapping starters to engage them a replacement is on the horizon.
Did you follow the starter alignment instructions when you replaced the starter? Are you getting oil on the Bendix? That could cause the starter gear to engage slowly. It is possible that the replacment starter has a problem. Also, if the previous starter had the same problem it could have damaged the gear on the flex plate.