Why would a Toyota relay only click when the key is turned but there are no dash lights and engine will not crank after alternator starter battery have been replace all fuses good?

Here are a few possible reasons why a Toyota relay might only click when the key is turned but there are no dash lights and the engine will not crank after the alternator, starter, battery, and fuses have all been replaced:

1. Incorrect Relay: Ensure the relay you replaced is the correct one for your Toyota model and year. A faulty relay or one with incorrect specifications can lead to these symptoms.

2. Faulty Wiring or Connections: Check the wiring and connections around the relay socket and the starter motor. Ensure all connections are secure, free of corrosion, and properly grounded.

3. Immobilizer System Issue: Some Toyota vehicles have an immobilizer system that prevents the engine from starting if the correct key or transponder is not detected. If there's an issue with the immobilizer system, it can cause the relay to click but prevent the dash lights and engine from functioning.

4. Ignition Switch Failure: A faulty ignition switch may not provide power to the relay or the necessary signals to other electrical components, resulting in the clicking sound without starting the engine.

5. Bad Starter: Even though the starter has been replaced, there might still be an issue with it, such as a faulty solenoid or internal damage.

To resolve this issue, it's recommended to take the vehicle to a trusted mechanic or auto electrician who can accurately diagnose the problem and perform the necessary repairs. If the problem persists after checking all these potential causes, there may be an underlying electrical issue that requires a comprehensive diagnosis.