Possible causes of electrical failure in a car
Battery
*Dead or faulty battery
* Battery terminal corrosion
* Loose or broken connections
Starter
*Failed starter
* Faulty retractor solenoid
*Wiring problems
Generator
* Faulty generator
*Wiring problems
* Alternator belt (if driven by a belt)
Electrical control module (ECU)
* Faulty ECU
*Wiring problems
*Software corruption
Fuses and relays
*Blown fuses
* Faulty relays
Wiring
* Damaged, exposed or broken wiring
* Loose or broken connections
* Incorrect installation of new components
Other reasons
* Faulty ignition switch
* Problems with the ignition switch
*Faulty door switch
* Faulty burglar alarm signal
Diagnosis steps
1. Check the battery.
*Measure the battery voltage using a voltmeter. It should be around 12.6 volts.
* Inspect terminals and connections for corrosion or looseness.
2. Try to start the car.
*If the starter does not turn, there may be a problem with the starter, battery or wiring.
*If the starter turns but the engine does not start, there may be a problem with the fuel system, ignition, or ECU.
3. Check fuses and relays.
* Locate the fuse box and inspect the fuses for blown fuses.
* Test the relays by connecting a tester to them.
4. Check wiring.
* Inspect the wiring for damage, exposure or breaks.
* Check connections for looseness or corrosion.
5. Use a diagnostic scanner.
* Connect an OBD-II scanner to your vehicle to identify trouble codes that may indicate specific electrical problems.
Precautions
* When working on vehicle electrical systems, always disconnect the negative terminal of the battery.
* Wear gloves and safety glasses to protect against possible sparks or burns.
* Do not use metal tools as they may cause a short circuit.
*If you are unsure of your abilities, seek professional help from a mechanic.