Mercedes W123 Battery Ground Cable Replacement

The ground cable on the W123 battery is very important to effective operation of its electrical system. Corrosion over time will reduce its effectiveness. Replace it, and consider improving the ground with a larger cable at the same time.

Bad grounds on the W123 can cause all sorts of issues, from hard starts, to erratic function of electrical components. One way to help reduce this issue is to replace the ground strap on your battery with a new one, and perhaps even one that is larger than the one from the factory.

Edit Step 1 Disconnect the battery  ¶ 

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Edit Step 1 Disconnect the battery  ¶ 

  • Start by disconnecting both battery terminals, beginning with the negative (-) side, which travels just a few inches to a bolt attaching the other end to the car's body.

  • Never remove your positive (+) cable first or you risk injury from electric shock.

Edit Step 2 Remove the old ground cable  ¶ 

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Edit Step 2 Remove the old ground cable  ¶ 

  • Loosen and remove this 13mm bolt that holds the cable to the metal of the car's chassis.

  • Now remove the old ground cable.

Edit Step 3 Install the new cable  ¶ 

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Edit Step 3 Install the new cable  ¶ 

  • You can see here that the new ground cable is substantially thicker. It is a 2 gage cable. The ends are also crimped better, protecting the inner wire from corrosion.

  • This cable is also a bit longer than the old one, giving some more wiggle room.

Edit Step 4  ¶ 

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Edit Step 4  ¶ 

  • Install the new ground cable, using the new captive bolt, and nut, that came with it.

Once you've finished, consider covering the terminal where the cable attaches to the battery in a silicone dielectric grease to prevent corrosion.

For more information, check out the Mercedes W123 device page.

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