This is on my '83 300SD. I have a similar problem with the warning lights - in particular the low fuel and alternator lights. With the key on all the lights go through self test. Wait for the glow plug light to go out and start - the low fuel and alt light come on really dim. I replaced the voltage regulator a few months back and I've rechecked voltage both static 12.3 VDC and 14.1 VDC once idle levels out. Could this be a broken solder path on the cluster? I've added a ground lead from the back of the cluster. I've also added a secondary ground (2ga) from the power steering bolt to the body.

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1983 300SD
1988 420SEL