Test Mercedes-Benz Alternator

Test Mercedes-Benz Alternator

Testing the alternator on a Mercedes Benz is relatively easy; it only takes half an hour, even for a beginner. This guide provides instructions on how to test the alternator on a Mercedes Benz.

In this vehicle, we already have replaced the alternator, but we’re still getting the battery warning light on the dashboard; there might be other issues like poor ground connection, blown alternator fuse, and sometimes an ECU problem.

We verify if the new alternator is working, test the alternator’s positive terminal for 12 volts, and check the feed in the voltage regulator.

What you will need


  • Voltmeter with an alligator clip
  • Wire (optional)
  • Electrical tape (optional)

Check Alternator Power

Alternator Positive terminal

Follow these steps to test the alternator on a Mercedes Benz.

First, we will check the positive terminal of the alternator, connect the positive test lead of the voltmeter to the alternator’s positive terminal, and connect the negative test lead to the ground from here.

Alternator Not Working

We read 12.93 volts, the battery voltage running to the positive alternator terminal. When the engine starts, the voltage should increase to 13 to 14.5 volts. With the engine off, the voltage should decrease to 11.5-12.9 volts.

Test Voltage Regulaor

Provide Signal to Voltage Regulator

Next, we will provide a signal voltage to the voltage regulator by hooking a wire from the battery directly to the signal terminal of the voltage regulator; we should see the voltage will increase in our voltmeter; the voltage may vary depending on the voltage required to charge the battery, the signal may provide 6 volts or full load, and that is 12 volts.

Alternator Fail test

Disconnect the alternator connector, connect the jumper wire to the voltage regulator’s signal terminal, and start the engine. While the engine is running, connect the other end of the jumper wire to the positive post; the voltage should increase to 14 volts.

Provide positive to voltage regulator

The voltage remains the same, so we have verified that the problem is our new alternator.

  • Please do not connect the jumper wire to the battery terminal for too long; remember that the signal terminal varies its voltage. The alternator might overload.
  • Consider checking your vehicle’s wiring diagram before performing the same procedure because, in some vehicles, the module provides a negative signal.

We hope you find the Test Mercedes-Benz Alternator guide helpful. Check these troubleshooting and repair guides for more help on your Mercedes-Benz.


  • Rushit Hila • ASE Certified

    Rushit Hila, an ASE-certified engineer (G1 Automotive Maintenance and Repair), brings over two decades of hands-on experience in the automotive world to his writing. With a strong educational background, including a Master of Science in Engineering and a Bachelor of Science in Engineering, he has honed his skills and expertise through years of practical work. As a respected authority in the field, Mr. Hila is dedicated to offering insightful and valuable content that resonates with both vehicle owners and mechanics.

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