2002 ford explorer has a no start problem

Ignition starter switch ???? It's Just a ignition switch ! If a problem with PATS - anti-theft system , the pcm will not supply a ground to the control side of the starter relay . Starter relay located in the central junction box , inside the vehicle fuse/relay box. Do you know what a relay is an how it works ? How to test electrical circuit's with a DMM - digital multi-meter ? Do you know what a wiring diagram is ? How to use one for testing electrical circuit's .
Free wiring diagrams here http://www.bbbind.com/free_tsb.html
Enter the vehicle info. year , make , model an engine size . Under system click on engine ,then under subsystem click on starting . Click the search button then the blue link .Do you have a manual or automatic transmission ? Also won't start if has a bad park neutral safety switch . Try putting into neutral an see if it will start then .
Testing for B+ voltage at pins # 30 & 85 . If you pull the relay an look at the bottom you will see four set's of numbers 30 & 87 ,30 is B+ voltage an 30 goes to the S terminal on the starter solenoid . 85 & 86 is control side of the relay ,one should have B+ voltage an the other is connected to the PCM . When the PCM supply's a ground the relay is energized closing the contacts inside sending battery voltage to the starter solenoid .
Are you confused yet ? Looking at the wiring will show what i just stated . Video's on youtube on testing relay's an their circuit's . Good luck .

Test the starter electrical circuits !
How to voltage drop test starter motor circuit Find a wiring diagram at http://www.bbbind.com/free_tsb.html . Enter vehicle info. Year , make , model and engine . Under system click on engine then under subsystem click on starting . Click the search button then the blue link. Buy a volt meter an test the control side of the circuit at the starter relay in the under hood fuse/ relay box . (BJB) .Do you know what an how a relay works ? Watch this youtube video .
VEHICLE RELAYS Operation Diagnosis This guy shows horn but starter relay works the same .

Will it turn over or no

You may have a bad starter solenoid. Could maybe be a bad relay also. Check your ground and power wires from your battery to make sure there are no breaks where it could be grounding out. Battery and starter may be good but bad wires won't let it get power to starter.

Try bypassing the Starter Relay. You can use a tool to jump across the terminals, but if you have a jumper cable just go from the battery side of the switch to the starter side.

There will be sparks, and the tool or cable will heat up, but if the Starter does not turn with normal speed; the Starter is bad or the main cable connection on the starter is corroded under the vehicle.

If the Starter does turn with normal speed, get a test light or Voltmeter and take off the small wire on the Relay post. Its usually in the middle of the Relay. Connect 1 end of your test equipment to a ground and the other to the small wire. Then turn the Ignition Key to Start. The test equipment should show power in the small wire.

If you have power in the small wire, then the Starter Relay is bad. The Relay is not connecting the power to the Starter. Replace the Relay.

You should be fixed by now. If you are not getting power to the small wire, you need to inspect the Interlock switch under the dash by the Brake pedal lever. There are 2 safety modes in your vehicle. The Interlock stops the starter from working if you are not in Park or Neutral. The switch is often hit by feet or gets out of adjustment through use. Adjust or replace the Interlock switch.

I hope my solution was very helpful in getting your vehicle running.

the neutral switch is located in the left side of the transmission and its connected to the shift cable.

Power doesn't go from the steering column to the starter ! When you turn the key to start it sends a voltage input to the PCM - engine computer . Then if fuse F2.4 5amp is good B+ voltage goes through the DTR - digital transmission range sensor , If the vehicle is in park or neutral to the starter relay . The PCM will turn on a ground to that circuit energizing the starter relay ! This will happen if there are no issues with the PATS system ! passive anti-theft syatem . Do know what a wiring diagram is ? Always look at a wiring diagram to find what all is involved in a circuit . Here is a web site for free wiring diagram's http://www.bbbind.com/free_tsb.html Enter vehicle info. year , make , model and engine size . Under system click on engine ,then starting in subsystem ! Click the search button ,then the blue link ! If you don't know about computer controlled systems suggest you take your vehicle to a qualified repair shop .
Watch videos on youtube for basic automotive electrical testing ! Never assume anything , learn how to test if you want to fix vehicles !

SOUND LIKE BAD STARTER.

Look for a ground wire that did not get hooked back up

starter relay is under hood on the drivers side fender area.

1. Disconnect the battery ground cable (14301).

1. Disconnect the starter motor solenoid relay switch wiring.
   1. Remove the protective cover.
   1. Disconnect the push-on electrical connector.
   1. Remove the nuts.
   1. Remove the cable.
   

Remove the starter motor solenoid relay switch (11450).
1. Remove the engine sensor/generator wires.
1. Remove the bolts and ground wire.
1. Remove the starter motor solenoid relay switch