To troubleshoot, you should:
1. Consult your owner's manual: This is the best resource to identify the fuse box locations (there are typically two – one under the hood and one inside the vehicle, usually under the dash) and a fuse diagram. Look for fuses related to the instrument panel, gauges, or possibly the PCM (Powertrain Control Module) if the issue is related to the electronic signals to the gauge cluster.
2. Check both fuse boxes: Carefully inspect all fuses in both boxes. Look for blown fuses (broken filaments or discoloration). Replace any blown fuses with fuses of the correct amperage (printed on the blown fuse and in the diagram).
3. Check the instrument cluster: If the fuses are fine, the problem might be within the instrument cluster itself. This would require professional diagnosis.
4. Consider the speedometer cable (if applicable): If your Explorer has a cable-driven speedometer, it's possible the cable is broken or disconnected. This requires inspecting the cable itself.
In short: There isn't a "speedometer fuse." The solution involves systematically checking fuses related to the instrument cluster and power distribution. Referencing your owner's manual is crucial for accurate fuse identification.