Possible reasons:
Battery problem:
*Dead or faulty battery
* Incorrectly connected battery terminals
* Battery terminal corrosion
Generator problem:
* Faulty generator
* Worn or torn alternator drive belt
* Alternator wiring problems
Wiring problem:
* Broken or damaged wires
* Poor connections or grounds
*Corrosion or rust on connectors
Fuse or relay problem:
*Blown fuses
* Faulty relays
* Poor contact in fuse box
Problem with the car computer (ECU):
*ECU damage or malfunction
* Problems with ECU software
Other possible reasons:
* Ignition switch malfunction
* Starter malfunction
* Immobilizer problems
* Signal system malfunction
Diagnostics and repair:
1. Check the battery. Measure the battery voltage using a voltmeter. The battery should show more than 12.6 volts. Clean the battery terminals and check for corrosion.
2. Check the generator. Start the engine and measure the voltage at the battery terminals. It should be above 13.5 volts. Check the alternator drive belt for wear or damage.
3. Check wiring. Inspect the wiring for breaks or damage. Check connections and grounds.
4. Check fuses and relays. Open the fuse box and inspect the fuses for blown fuses. Remove and check the relay.
5. Checking the car computer (ECU). A professional scan may be required to diagnose ECU problems.
6. Look for other possible causes. Check the ignition switch, starter, immobilizer and alarm system.
If you are unsure about diagnosis or repair, contact a qualified mechanic.