1. Check the Fuse:
- Locate the fuse box, typically under the hood or inside the cabin.
- Identify the fuse labeled "Speedometer" or "Instrument Cluster."
- Check if the fuse is blown. If it is, replace it with a fuse of the same amperage.
2. Inspect the Speed Sensor:
- The speed sensor is usually mounted on the transmission or differential.
- Look for any damage to the sensor or its wiring.
- Clean the sensor and its connector to ensure proper contact.
3. Test the Speedometer Cable:
- The speedometer cable connects the speed sensor to the speedometer gauge.
- Disconnect the cable from the speedometer and check if it rotates smoothly.
- If the cable is damaged or does not rotate smoothly, replace it.
4. Check the Speedometer Gear:
- The speedometer gear is located inside the transmission or differential.
- Inspect the gear for damage or wear.
- If necessary, replace the speedometer gear.
5. Verify the Ground Connection:
- Ensure the ground connection for the speedometer is clean and secure.
- A poor ground connection can cause erratic speedometer readings.
6. Test the Speedometer Gauge:
- Disconnect the speedometer cable from the gauge and use a handheld drill or similar tool to spin the cable.
- Observe the speedometer needle. If it doesn't move or moves erratically, the gauge may be defective and need replacement.
7. Check for Instrument Cluster Issues:
- If all the above components seem functional, there may be an issue within the instrument cluster itself.
- Some RX-7 models have circuit boards or electronic components that can fail, affecting speedometer functionality. Consider seeking professional help for further diagnosis and repair of the instrument cluster.
Note:
- If you're not comfortable with these troubleshooting steps or encounter any issues, it's best to seek assistance from a qualified mechanic or automotive electrician familiar with the Mazda RX-7. Speedometer problems can be caused by various factors, and professional expertise may be necessary for accurate diagnosis and repair.
