Use a charged battery for testing.
Set the ammeter to the highest scale (0.5 mA to 0.5 A). Remove the ground wire from the battery. Place an ammeter between the negative battery terminal and the ground wire. Connect the positive lead of the ammeter to the removed battery ground wire, and the negative lead of the ammeter to the negative battery terminal.
Note: This test can also be carried out using a test lamp. If a lamp connected between the removed wire of a grounded battery and the negative terminal of this battery does not light up, an ammeter will also need to be used.
Turn off all electrical consumers, disconnect the electric clock and close the car doors.
Switch from amp to milliamp scale until a reading is obtained (allowed leakage current equal to 1-3 mA). Removing alternately, one after another, fuses, interrupt various circuits. If, when removing any of the fuses, the ammeter reading becomes zero, it will be clear that there is a leak in the circuit that is currently open. Sources of malfunction can be rusty and dirty contacts, wires with worn braid, internal short circuits in blocks.
If no current is observed in the electrical circuit, then the connections of bare elements should be removed: this may be a starting device (starter), alternator or ignition system.
Connect the battery again.