Possible Causes:
* Faulty Starter Motor: This is the most common culprit. A seized or internally shorted starter motor draws excessive current, blowing the fuse.
* Short Circuit in Starter Wiring: Worn, frayed, or pinched wiring between the battery, starter solenoid, and starter motor can cause a short circuit, leading to a blown fuse. Look for damage near the starter itself, which is often located on the engine block near the transmission bellhousing.
* Faulty Starter Solenoid: The solenoid is the electromagnetic switch that engages the starter motor. A faulty solenoid can draw excessive current or fail to disengage properly.
* Problem with the Neutral Safety Switch: This switch prevents the starter from engaging unless the transmission is in Park or Neutral. A faulty switch might allow continuous current flow, even when the key is turned off, leading to a blown fuse.
* Excessive Battery Drain (less likely): While less probable, a significant parasitic draw on the battery could cause the starter circuit to draw too much current when the ignition is engaged, blowing the fuse.
Troubleshooting Steps:
1. Check the Fuse: Before anything else, visually inspect fuse 102. Make sure it's truly blown. Replace it with a fuse of the *same amperage rating* (it should be printed on the fuse itself). Do *not* replace it with a higher amperage fuse.
2. Test the Starter Motor (Difficult): This usually requires professional tools. If you have a multimeter and some mechanical experience, you can attempt to test the starter motor for continuity and shorts. However, it's best to leave this step to a mechanic if you're unfamiliar.
3. Inspect the Wiring: Carefully examine the wiring harness leading to the starter motor for any signs of damage, such as fraying, melting, or corrosion. Pay close attention to the area near the starter itself, where wires are often subject to wear and tear.
4. Test the Starter Solenoid (Difficult): Testing the starter solenoid also requires a multimeter and understanding of basic electrical testing. It involves checking for continuity and voltage across the solenoid terminals. Again, leave this to a mechanic if you're not comfortable.
5. Check the Neutral Safety Switch: This switch is usually located near the transmission. You can test it with a multimeter by checking for continuity in the correct gear positions (Park and Neutral). A faulty switch needs replacement.
6. Battery Test (Less likely): Have your battery tested to rule out a high parasitic draw or a weak battery that's struggling to provide enough current.
Important Note: If the fuse blows immediately after replacing it, *do not keep replacing it*. This indicates a serious electrical short that needs to be diagnosed and repaired by a qualified mechanic before further damage occurs. Continuing to replace the fuse could damage the wiring harness or even cause a fire.
If you are not comfortable performing these steps yourself, it is strongly recommended to take your 2003 Ford Expedition to a qualified mechanic or auto electrician for diagnosis and repair. Attempting repairs without proper knowledge and tools can lead to further damage or injury.
