Testing Current Drain

If tests show that the alternator and regulator are operating correctly, but the battery still continually runs down, there may be a short in the electrical system causing a continuous current drain.

To test for current drain, turn off the ignition switch, the radio, and all lights. Disconnect the clock, if so equipped, by removing its fuse. Turn on the switches for the heated rear window and, if applicable, the air conditioning; this will determine if the load reduction relay is faulty. Disconnect the negative (-) cable from the battery and connect a test light between the cable and the negative post. If the test light comes on, some electrical accessory or a short in the electrical system is draining current from the battery. Isolate the faulty circuit by removing and replacing the fuses one at a time. When the test light goes out, the circuit with the short is located. If no fault is found in this way, a fault may exist in the components without fuses, such as the alternator, the starter motor, the ignition system, and the instrument cluster. Disconnect the items one at a time until the test light goes out.