2001 Ford explorer sport Trac

Make sure battery has a full charge and battery cables/connections all good. That means using a digital multimeter across battery posts, eveything off, the generic spec for a full charge, 12.6 volts. You can leave meter leads touching battery posts, have helper turn key to crank, the voltage reading shouldn't drop below 9.6 volts, that's a generic spec. If the reading drops way down there, that's not going to work. Another issue, the voltage reading doesn't drop much, if at all, that usually means an open circuit, somewhere. note the diagram, click on the link to enlarge. The starter motor has two voltage circuits, one comes from the battery, hot all the time. The other terminal goes hot when relay is energized. The starter motor grounds through engine block. You can see the two fuses at the top, check when problem ongoing, Use a test light and voltage at fuse. See the relay, for testing, you can unplug relay, use jumper wire between cavities on load side, left side in diagram, terminals 30 and 87. Terminal 30 is fuse protected and hot all the time. If you try this, make sure transmission is in park or neutral and parking brake is set. Make sure vehicle can't move? The diagram said early production, as you can see, the security system can kill the starter relay, meaning, no starter motor action.

check to make sure you have a good ground from the battery ground post to the vehicle. One is usually from the battery ground to the engine and this grounds the starter. If this ground is poor the starter is not grounded and will not turn over and engage the starter Bendix from the starter ignition switch, starter relay or solenoid.