* Low Battery Voltage: This is the most common cause. A weak battery can't provide enough power to fully engage the starter motor. Have the battery load tested at an auto parts store. Even if it shows a somewhat decent voltage, it might not have enough *cranking amps* to turn the starter.
* Bad Starter Motor: The starter itself could be failing. The clicking might be the solenoid within the starter trying to engage, but not having enough power to fully spin the engine. This is less likely if the clicking is coming from the relay *before* the starter motor itself.
* Corroded or Loose Battery Cables: Check the battery terminals and the cables leading to the starter and the body of the car. Clean them thoroughly with a wire brush and baking soda and water solution. Tighten the connections. Corrosion restricts current flow.
* Faulty Ignition Switch: A failing ignition switch can prevent power from reaching the starter. This is less likely if you're getting a relay click.
* Wiring Issues: There could be a broken or corroded wire somewhere in the circuit between the battery, ignition switch, relay, and starter. This requires careful visual inspection of the wiring harness.
* Neutral Safety Switch (NSS): This switch prevents the car from starting unless it's in Park (automatic) or Neutral (manual). A faulty NSS won't allow the starter circuit to complete.
* Incorrect Relay Replacement: Though you replaced the relay, it's possible you got a bad replacement or installed it incorrectly. Double check the relay's placement and that it's the correct part for your vehicle.
Troubleshooting Steps:
1. Battery Test: This is the absolute first thing to do.
2. Cable Inspection and Cleaning: Thoroughly clean and tighten all battery and starter cables.
3. Visual Inspection of Starter: Look for any obvious damage or corrosion on the starter motor itself.
4. Check Neutral Safety Switch (if applicable): Make sure the car is in Park (automatic) or Neutral (manual). Try gently moving the shifter to ensure the NSS is engaging correctly.
5. Relay Placement: Confirm the relay is correctly seated.
If you've checked these and the problem persists, you'll likely need a professional mechanic to diagnose the issue. They have the tools and expertise to test the starter, ignition switch, and wiring harness more thoroughly. Describing the exact location of the clicking (relay or starter) will help them.
