* Parasitic Drain: Something in the car's electrical system is drawing power even when the car is off. This could be anything from a faulty dome light switch, a malfunctioning radio, a short circuit in the wiring harness, or even a bad alternator diode. A parasitic drain slowly discharges the battery overnight or even over a few hours.
* Alternator Failure: The alternator is responsible for charging the battery while the engine is running. If it's not generating sufficient power, the battery won't recharge, leading to voltage loss and stalling. This is especially likely if the problem occurs only while driving.
* Bad Battery Connections: Loose or corroded connections at the battery terminals or elsewhere in the electrical system will prevent proper charging and lead to voltage drops. Even a new battery needs clean, tight connections.
* Voltage Regulator Problem (part of the alternator): The voltage regulator controls the alternator's output. A faulty regulator can overcharge or undercharge the battery, leading to premature failure or voltage drops.
* Starter Motor Issues: A faulty starter motor can draw excessive current, quickly depleting the battery. This is more likely to cause immediate stalling rather than a gradual voltage drop.
* Faulty Wiring: A short circuit in the wiring harness can cause a significant drain on the battery.
Troubleshooting Steps:
1. Check Battery Connections: Clean the terminals with a wire brush and ensure they are securely fastened.
2. Test the Battery: Use a multimeter to check the battery's voltage when the engine is off and then when it's running. A low voltage even when running indicates a charging problem.
3. Test the Alternator: Have the alternator tested at an auto parts store. This is usually a free service.
4. Measure Parasitic Drain: This requires a multimeter and some knowledge of automotive electrical systems. Disconnect the negative battery terminal and measure the current draw. Any significant current draw (more than 50 mA) indicates a parasitic drain.
5. Inspect Wiring: Look for any signs of damage, corrosion, or fraying in the wiring harness.
Important Note: Working on a car's electrical system can be dangerous. If you're not comfortable performing these tests yourself, take the car to a qualified mechanic. They have the tools and expertise to diagnose the problem accurately and safely. A classic car like a 1988 Seville may have some unique electrical quirks.
