* Dead battery: Even if the car starts, a weak battery might not have enough power to run accessories. This is a common cause. Test the battery voltage with a multimeter.
* Bad alternator: The alternator recharges the battery while the engine is running. A faulty alternator won't recharge the battery, and might not supply enough power to the accessories even when running.
* Blown fuse(s): A blown fuse will cut power to a specific circuit, such as the lights or radio. Check the fuse box(es) in your car for any blown fuses (look for a broken filament inside).
* Faulty accessory switch(es): The switch itself might be broken and not completing the circuit.
* Wiring problem: Damaged or corroded wiring can prevent power from reaching the accessories. This could be anywhere from the battery to the accessory.
* Bad ground connection: A poor connection to the car's ground (negative battery terminal) can prevent proper electrical flow.
* Faulty power distribution module/fuse box: This is less common, but a problem with the main component distributing power could affect multiple accessories.
What to do:
1. Check the battery voltage: Use a multimeter to measure the battery voltage with the engine off and then running. A low voltage indicates a weak battery or alternator problem.
2. Check the fuses: Carefully inspect all relevant fuses.
3. Try different accessories: See if *any* accessory works. If some work and others don't, it points towards a specific circuit problem (blown fuse, wiring, switch).
4. Listen for clicking sounds: When you try to turn on an accessory, listen closely. Clicking may indicate a relay problem.
If you're not comfortable checking these things yourself, take your car to a mechanic for diagnosis and repair. It's safer to let a professional handle electrical issues.
