Introduction

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.

Tools

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.
  • 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.

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

  • Now remove the old ground cable.

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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.
  • 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.

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

after replacing this ground cable my tach started working again! I can’t say enough about cleaning grounds and contacts/connections in general.  A cheap and easy way to solve some common electrical issues

Bob - Reply

Conclusion

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

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Nicolas Siemsen

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