* Speed Sensor Problems: This is the most common culprit. The vehicle has one or more speed sensors that send signals to the instrument cluster. A faulty sensor can be caused by:
* Wiring issues: Broken, frayed, or corroded wires leading to the sensor(s). Check for damage near the transmission and wheel wells.
* Sensor failure: The sensor itself might have gone bad due to age, wear, or damage from debris or water. The Vehicle Speed Sensor (VSS) is the most likely candidate, often located near the transmission. There might also be a separate sensor in the wheel speed sensor system.
* Sensor connector problems: Corrosion or poor connection at the sensor's connector.
* Instrument Cluster Problems: The speedometer is part of the instrument cluster. Problems here could include:
* Internal failure: A component within the cluster itself may have malfunctioned. This is often harder to diagnose and repair than sensor issues. It could need repair or replacement.
* Faulty circuit board: The circuit board in the cluster can suffer damage or corrosion.
* Loose connection: Check all connections within the cluster itself.
* Transmission Problems: While less likely to be the *direct* cause of a speedometer failure, a problem within the transmission itself (like low transmission fluid) can sometimes interfere with the sensor's ability to function properly.
* PCM (Powertrain Control Module) Issues: The PCM receives signals from the speed sensor and interprets them. A malfunctioning PCM can prevent the information from reaching the instrument cluster. This is less common than sensor problems.
Troubleshooting Steps (in order of increasing difficulty):
1. Check the fuses: Ensure all fuses related to the instrument cluster and speed sensors are intact. Consult your owner's manual for fuse box locations and diagrams.
2. Inspect wiring: Carefully examine the wiring harness leading to the speed sensor(s) for any visible damage, breaks, or corrosion. Pay close attention to areas that experience movement or vibration.
3. Clean sensor connectors: Disconnect and clean the connectors at the speed sensor(s) with electrical contact cleaner. Reconnect them securely.
4. Check the speed sensor(s): This may require some mechanical skill. Accessing the sensor(s) might involve getting under the vehicle. You might need a multimeter to test the sensor for proper voltage and resistance, comparing it to specifications in a repair manual. Replacing the sensor is often the solution.
5. Scan for diagnostic trouble codes (DTCs): Use an OBD-II scanner to read any trouble codes stored in the PCM. This can pinpoint the problem area.
6. Check the instrument cluster: If all else fails, the instrument cluster itself might be at fault and might require professional diagnosis or replacement.
Remember to consult a repair manual specific to your 2000 Ford Windstar for detailed information on sensor locations, wiring diagrams, and diagnostic procedures. Trying to fix electrical issues without proper knowledge can lead to further damage. If you're not comfortable working on your vehicle's electrical system, it's best to take it to a qualified mechanic.
