Use a charged battery for testing.
1. Disconnect the ground (–) cable from the battery terminal.
Attention! This erases all accumulated data in electronic storage devices, such as the radio anti-theft code. Before disconnecting the battery, you should also read the recommendations in the subsection 13.1.7.
2. Set the ammeter (measurement range from 0–5 mA to 5 A) to the maximum measurement limits. Connect the ammeter between the negative battery terminal and the wire connecting its terminal to the car body.
Attention! The test can also be carried out using a test lamp. But if the lamp does not light when it is connected between the flexible jumper and the negative pole of the battery, then in any case you need to use an ammeter.
3. Turn off all current consumers, disconnect the electronic clock from the terminals (constant current consumer), close the doors.
4. By switching the ammeter ranges, determine the current value.
5. When removing fuses, open various electrical circuits in sequence. If zero is indicated in one of the broken circuits, this is where you need to look for the source of the malfunction. Defects can be correlated or dirty contacts, completely worn wires, internal short circuits in the units.
6. If no defects are found in the electrical circuits protected by fuses, then the wire tips should be pulled off the units not protected by fuses. These are: the ignition system, the generator and the starter.
[Original material on the website: Mercedesman.ru]
7. If the indication returns to zero when disconnecting one of the unprotected units from the terminals, repair or replace the corresponding part. If a current leak is detected in the starter or ignition system, first check the ignition switch according to the electrical circuit diagram.
8. Connect the ground (–) wire to the battery terminal.
9. Set the time and also enter the anti-theft code for the radio.