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Hello I will help you with your question,
A couple of questions;
How do you know the starter and battery are good?
When you checked for power to the starter did you check the small wire at the solenoid for power when you turn the key to the start/crank position?
Can you turn the engine over by hand with a socket wrench on the crank pulley?
Your starter may have failed or the engine may be locked up.
Have you driven through any deep water or had any starting problems before this?
Let me know the answers to my questions and I can tell you why your engine does not crank when you turn the key
engine not locked, will turn. had someone turn key to start position with my meter on solenoid wire. yes other end grounded.no control power. jumped hot wire over on solenoid, starter kicked. three month old battery, put meter on it 12.8 volts. didn't change voltage none when putting in start position. no water drivethrough. car did this three days in a row. then started later. before finally stopping all together. when it is in dead mode (now) and the last two times, it has a small humm at the back of the engine compartment. when it does start, you turn off with key in power position it doesn't do this. when it's dead and not starting it humms
Ok then I have a much clearer picture of what is happineng,
There is no relay in this sytem so when you turn the key power goes to the neutral safety switch on the clutch pedal arm or through the range switch mounted on your transmission before going to the starter solenoid.
If you have no power at the solenoid when you turn the key to the crank position try using a large paperclip to jump the switch. Jump from the blue to the blue wire if you have a manual transmission or from the blu to the red wire if you have an automatic.
The hum you hear may be the starter solenoid so you will have to be sure you have a good connection from the battery to the starter by measuring from the battery positive post to the large terminal at the starter while cranking, you should not have more than 0.5volts between these two points while cranking. If you have more the connections or the cable are faulty and need attention. This must be done while cranking.
Let me know what you find with these two tests
The blue wires are on the switch at the clutch pedal arwm if you have a manual transmission or on the range switch that is mounted on the top of the transmission if this is an automatic (the wires are red and blue in that case)
You can also use the paperclip as a point to measure the voltage as you turn the key by inserting it from the backside of the connector along the wire. If you have voltage at the paperclip you should have voltage to the starter solenoid.
Be careful as if you jump the switch while the transmission is in gear and the starter motor turns the engine the vehicle will move.
I'm guessing from your description that you have an automatic transmission?
Connect from pin #9 (blue) to pin #6 (red) in the range switch connector diagram posted below
If nothing happens and you get power to the small starter post check the large battery cable and run a jumper cable from the positive post to the large starter terminal if needed. If the starter still won't turn you need to replace the starter as it has a dead spot.
If you jump from the battery cable to the small terminal on the solenoid does the starter spin the engine? Be sure you are in park or neutral before you do this.
Also do you get power to the small terminal without the jumper in the range switch?
I'm a little confused also you are using a screwdriver to jump from the "B" terminal to the "ST" terminal in this diagram and the starter spins AND spins the engine?
Ok then the "ST" terminal has to be jumped to the "B" terminal to energize the pull in winding, this moves the gear on the end of the starter into contact with the ring gear on the flexplate of the engine so that when the starter motor turns it will turn the engine. When the pull in winding moves the gear it also moves a contact plate to connect the "B" terminal to the "M" terminal which is what you are doing when you jump the two large terminals.
So you know the motor turns but you dont know if the solenoid is good.
Put the jumper back in the range switch and jump power to the paperclip, if the starter does not turn and you are getting power to the small "ST" terminal replace the starter as the solenoid has failed. You can replace just the solenoid but the cost is almost as much as a starter and I doubt that you could find one in a parts store.
Let m eknow if this checks out.