Checking the generator and voltage regulator on the car (Mercedes-Benz E-Class W123)

To determine the cause of insufficient battery charging, perform the following test of the voltage regulator.

1. Disconnect the wire from the negative battery terminal.

2. Connect a voltmeter with a measurement range of 0-16 V between the B+ terminal of the generator and the generator housing.

3. Disconnect the red wire from the B+ terminal and connect an ammeter with a measurement range of 0-60 A between the tip of the wire and the terminal.

4. Connect the wire to the negative terminal of the battery and provide a 55A load using a load rheostat.

5. Start the engine and set a constant speed of 2000 to 3000 rpm.

6. Adjust the battery current from 23 to 30 A with the load rheostat, while the voltmeter readings should be from 13.9 to 14.8 V. Any deviation from these limits requires immediate inspection of the voltage regulator by a company representative (or its replacement).

7. To check the generator output power, connect the load rheostat, set the engine speed to 1300 rpm and simultaneously increase the load current to 10 A. The battery charge indicator lamp should not light.

8. Repeat the test at 2000 and 6000 rpm engine speed, setting the load current to 36 and 55 amps for a 55-amp alternator or 43 and 65 amps for a 65-amp alternator.