Introduction

After many decades the grounds of your W123's electric system may become corroded. Cleaning them up can help fix or prevent a variety of electric gremlins that can crop up on an older car. Learn to maintain several of these grounds with this guide.

The primary ground for your car's electric system is the ground on the car's battery. It connects to the chassis of the car next to the battery itself.
  • The primary ground for your car's electric system is the ground on the car's battery. It connects to the chassis of the car next to the battery itself.

  • Begin by disconnecting the ground or negative terminal from your battery. For guidance on removing the terminal, and for other suggested battery maintenance while it is disconnected, click here to see the battery maintenance guide. Follow the cable to the attachment point on the chassis; it will be very nearby.

  • Loosen and remove the nut that holds the battery ground cable to the chassis, which will allow you to set aside the cable for now.

  • Use some emory cloth, very fine sandpaper, or a soft metal brush such as brass to remove any dirt or corrosion from the area where the battery cable connects to the chassis. Then re-install the cable and reconnect it to the battery.

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Next find the ground connection for many of the other electric components under the hood of your car, such as your headlights and turn signals.
  • Next find the ground connection for many of the other electric components under the hood of your car, such as your headlights and turn signals.

  • This set of ground connections is usually just behind the left/passenger's side turn signal. If you do not find it there you can look around the rest of the engine compartment. Keep in mind that on a Mercedes-Benz of this era ground cables should all be brown in color as shown.

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Loosen this ground connection. You will need to remove the turn signal to reach the nut on the back of the bolt that holds those ground wires. For guidance on removing the turn signal click here to review the turn signal bulb replacement guide. Just as you did for the main battery ground clean the area where these wires connect to the chassis. Just as you did for the main battery ground clean the area where these wires connect to the chassis.
  • Loosen this ground connection. You will need to remove the turn signal to reach the nut on the back of the bolt that holds those ground wires. For guidance on removing the turn signal click here to review the turn signal bulb replacement guide.

  • Just as you did for the main battery ground clean the area where these wires connect to the chassis.

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While the connections are loose you can also clean the ends to ensure a good electric current.
  • While the connections are loose you can also clean the ends to ensure a good electric current.

  • Re-attach these wires.

  • There are more ground wires than these on the car. The theory applies to them all. Continue to maintain any other ground wires you find in the trunk, under the car by the transmission, behind the dash.

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Conclusion

To reassemble your device, follow these instructions in reverse order.

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Nicolas Siemsen

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2 Comments

Have dielectric grease on hand ... it is NOT conductive .... after reassembling things, put dielectric grease, lightly, over everything....might cut down corrosion happening so fast again ....'thanks for idea from well known source of Mercedes info, elsewhere.

I have a "mystery" starting motor problem and hope re-newing ground and power connections fix it, instead of the solution being the whole starter motor replacement.

For 10-50-sometimes 100 start ups, everything's fine ... but then, usually after engine is hot and I've driven awhile, then stop, turn engine off...then it acts as if there's a "dead" spot on a copper wires winding set-up ..... it always DOES start... I just try it about 20 seconds later...once, twice, usually no more than 3 or 4 times, then it starts up normally. ......... I've replaced my battery GROUND cable--that's easy to get to....the power cable to the starter motor is next.

christopherchrishaskell - Reply

clean until shiny and apply dielectric grease. On computer autos this is even more important. Gary

gvonneida - Reply

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