How to repair electrical issues causing battery drain in the 2015 Mazda MX-5 Miata (NC)?

1. Identify the Source of the Drain

• Start by ensuring that the battery is fully charged.
• Use a multimeter set to measure amperage. Disconnect the negative battery cable and place the multimeter in series between the negative battery post and the disconnected cable.
• Check the current draw on your multimeter. A normal draw is typically less than 50 milliamps. If it’s higher, you have a parasitic drain.

2. Isolate the Circuit

• Start pulling fuses one at a time while monitoring the multimeter. When the current draw drops to normal levels, you have identified the circuit causing the drain.
• Refer to the Miata's owner's manual to identify which components are on the problematic circuit.

3. Inspect Components on the Problematic Circuit

• Check each component on the identified circuit for visible damage, corrosion, or loose connections.
• Pay particular attention to common culprits like the alternator, stereo system, and any aftermarket electrical accessories.

4. Repair or Replace Faulty Components

• If you find a component that appears to be faulty, disconnect it and check if the parasitic drain stops. If it does, repair or replace the faulty component.
• Common repairs might include replacing wiring, connectors, or the component itself.

5. Check the Battery Health

• Even if you find a faulty component, it’s a good idea to test the battery’s health given that a draining issue might have weakened it. Use a battery tester to check its state-of-charge and condition.
• If the battery is weak or failing, replace it to ensure the electrical system functions properly.

6. Test the Charging System

• Ensure the alternator is charging the battery correctly. Use a multimeter to check the voltage at the battery terminals with the engine running; it should be between 13.7 to 14.7 volts.
• If the voltage is outside this range, have the alternator checked and, if necessary, replaced.

7. Preventative Measures

• After resolving the issue, consider installing a battery maintainer if the car sits for extended periods.
• Regularly check connections and condition of the battery and charging system during routine maintenance.
• If you have aftermarket accessories, ensure they are wired correctly and not drawing power when the vehicle is off.

By following these steps, you should be able to identify and repair electrical issues causing battery drain in your 2015 Mazda MX-5 Miata (NC).