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Old 03-19-2019, 07:00 PM
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W123 Ground Locations?

Going to start troubleshooting some minor electrical problems in the '85 300 CD. First thing to start with is to go over the major chassis grounds. There is one by the right headlight, and the engine ground strap under the oil filter housing. Can anybody tell me where the other chassis grounds are located?

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Old 03-19-2019, 07:19 PM
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Ground wires are the color brown and several of them are located behind the instrument cluster. The wires are attached to the steering column support. The instrument cluster can be removed by using a wire (coat hanger) that has been fashioned into a piece with a gentle hook on one end of the wire. Insert the hook end behind the instrument cluster one end at a time. Using a pair of vice grips to pull on the wire gently pull the cluster towards the rear of the car alternating from one end to the other. Once you have the cluster out far enough disconnect the Speedometer cable and the wiring harness from the rear of the cluster. Using a 10mm wrench disconnect the oil pressure gauge line. From there you can pull the cluster out and unplug the remaining wires. Do not crank the engine while the cluster is out - you will have oil everywhere. To reinstall reattach everything disconnected and gently push the cluster back into the dash. It is a friction fit.
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Old 03-19-2019, 09:34 PM
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IIRC there are several under one bolt close to the battery on the fenderwell and another set near the antenna on the wheel arch inside the trunk.

You may consider adding some grounds also to the engine block.

Good luck!!!
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Old 03-19-2019, 10:51 PM
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I have attached a ground from the battery or cable to a bolt on the starter, when the starter acts up and nothing else will fix the problem. The ground through the aluminum engine/transmission adapter may get corroded.
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..I also have a 427 Cobra replica with an aluminum chassis.

Last edited by t walgamuth; 03-20-2019 at 05:00 AM.
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Old 03-20-2019, 12:46 AM
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If you're looking for a ground location for the instrument cluster, there are two bolts that sit behind the cluster that hold steering jacket to the frame.

You can unbolt one of these and thread a ground strap from the cluster to this bolt. Works very well for a ground. I run the strap from one of the bolts that attach the spedo to the fuel, coolant, and oil pressure guage. Any autoparts store will sell a nice ground strap for this purpose.
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Old 03-21-2019, 03:13 PM
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Quote:
Originally Posted by carock View Post
Going to start troubleshooting some minor electrical problems in the '85 300 CD. First thing to start with is to go over the major chassis grounds. There is one by the right headlight, and the engine ground strap under the oil filter housing. Can anybody tell me where the other chassis grounds are located?
LH headlight, RH headlight, behind cluster, & LH rear wheel arch.

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