Possible Causes:
* Faulty Ignition Switch: This is the most common suspect. The switch itself might be malfunctioning, sending power to the starter even when the key isn't in the "start" position.
* Wiring Issues: Damaged, frayed, or shorted wires in the ignition system can cause power to reach the starter inappropriately. This could be anywhere from the ignition switch to the starter motor itself. A common area to check is the wiring harness near the steering column.
* Starter Solenoid: The solenoid is an electromagnetic switch that engages the starter motor. A faulty solenoid might be sticking or activating prematurely.
* Neutral Safety Switch (NSS): This switch prevents the vehicle from starting unless it's in Park (or Neutral, depending on the transmission type). A faulty NSS could be sending the wrong signal.
* Aftermarket Alarm or Immobilizer System: A poorly installed or malfunctioning aftermarket security system could be interfering with the ignition system.
* Faulty BCM (Body Control Module): The BCM manages various electrical functions. A malfunction could lead to unusual behavior, including unintended starter engagement.
Troubleshooting Steps (In Order of Ease):
1. Check the Ignition Switch: Carefully examine the ignition switch for any signs of damage or wear. Try wiggling the key gently while in the "off" position to see if the issue is intermittent. This is a difficult component to replace yourself and often requires specialized tools.
2. Inspect Wiring: Visually inspect the wiring harness leading to and from the ignition switch, starter, and neutral safety switch. Look for any obvious damage, corrosion, or loose connections. Pay close attention to the area around the steering column.
3. Test the Neutral Safety Switch (NSS): This will require a multimeter and some knowledge of automotive electrical systems. You'll need to test the continuity of the switch in different gear positions. A faulty NSS often prevents starting, but can sometimes cause erratic behavior.
4. Check the Starter Solenoid: You can tap the solenoid gently with a wrench (while the key is off!) to see if the problem is intermittent. However, this is not recommended for someone without experience.
5. Disconnect Aftermarket Accessories: If you have an aftermarket alarm or immobilizer, temporarily disconnect it to see if that resolves the problem.
Important Safety Considerations:
* Disconnect the battery negative terminal before undertaking any electrical work to prevent accidental shorts or injury.
* If you're not comfortable working with automotive electrical systems, take your Expedition to a qualified mechanic. This is a potentially dangerous problem that could lead to injury or further damage if not handled correctly.
Attempting to fix this without experience can be risky. If the car is trying to crank when the key is off, you risk damaging the starter motor or battery, and it's a potential fire hazard. Professional help is recommended.
