A quick check for bad grounds is to connect a test light in parallel with the suspect ground.

As an example, clip the test lights alligator clip to the engine block and touch the probe to the battery post. Be sure you are on the post and not the terminal. Have someone turn on a high draw item such as the high beams or attempt to start the engine. The test light should not glow at all.

You can also use a voltmeter the same way. Set it on DC volts with a range that will handle 12 volts. You should not see much over a few millivolts with headlights and no more than 1 volt with the starter.

Michael

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Usta haves '69 250/8, '76 280C, 1971 250C 114.023, 1976 450SEL 116.033
Current have, 1983 300SD 126.120