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  #1  
Old 02-19-2014, 09:30 PM
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Dash cluster grounding

I'm having an intermittent problem that fuel shows full even if it isn't, temp shows 120*C+, both turn signal and some other cluster warning lights turn on and stay bright. I'm guessing this is a symptom of a bad/loose ground wire on the cluster.

Car is a 1983 W123. How do I access and tighten said wire?

Thanks in advance...

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Old 02-19-2014, 10:23 PM
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Originally Posted by spdrun View Post
I'm guessing this is a symptom of a bad/loose ground wire on the cluster.
That might not be such a good guess. I fail to understand how a poor ground connection could cause the conditions that you report.
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Old 02-19-2014, 10:35 PM
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Originally Posted by tangofox007 View Post
That might not be such a good guess. I fail to understand how a poor ground connection could cause the conditions that you report.
Cluster is trying to find a ground via the turn signal/high-beam/glow-plug lights. I'm guessing that the lack of a good ground reference is also messing with the instrument panel voltage regulator in some manner.

Pretty much the ONLY explanation for this set of unrelated failures. Now again -- how the cluster ground wire accessed?
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Old 02-19-2014, 10:44 PM
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Originally Posted by spdrun View Post
Now again -- how the cluster ground wire accessed?
Pull the cluster out and you will have complete access to all its wiring.

Quote:
Originally Posted by spdrun View Post
I'm guessing that the lack of a good ground reference is also messing with the instrument panel voltage regulator in some manner.
If you could post a picture of the instrument panel voltage regulator, that would be great.
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Old 02-19-2014, 10:54 PM
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Which wire is it? (color/location)
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Old 02-19-2014, 11:07 PM
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Generally if you have a bad ground on the instrument cluster the 12 v gauges (fuel and temp) the gauge needles will flicker. I had this happen on my 85 300d. I solved the problem by adding a new ground wire from the back of the cluster to the cluster of other ground wires (brown) bolt behind the cluster.

Last edited by BWhitmore; 02-19-2014 at 11:43 PM.
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Old 02-19-2014, 11:12 PM
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Originally Posted by spdrun View Post
Which wire is it? (color/location)
Brown wire, C151 connector.
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Old 02-19-2014, 11:33 PM
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The only voltage regulator is on the alternator....all the gauges are 12v....so there are no regulators behind the dash.

Location of grounds

Two huge bundles behind cluster
One behind passenger tail light
One under sunroof motor/antenna motor
Chassis to trans bell housing under drivers side
Battery to chassis
One behind passenger head light
One by gear shifter

All are brown wires..

Remove your cluster and inspect for any burned traces too
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Old 02-20-2014, 12:25 AM
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Just run a jumper from one of the back screws (ones into the metal backing plate) to a chassis location behind the cluster. Screwy grounds can be a common w123 cluster issue. Just solve it by making a solid ground rather than repairing what's already there.
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Old 02-20-2014, 09:14 AM
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Screwy grounds can be a common w123 cluster issue.
Kindly explain how "screwy grounds" could cause turn signal and other annunciator lights to illuminate.
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Old 02-20-2014, 03:57 PM
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Originally Posted by tangofox007 View Post
Kindly explain how "screwy grounds" could cause turn signal and other annunciator lights to illuminate.
The turn signal annunciator lights are wired between ground and the positive line to the turn signals. If ground isn't tied to ground and the signals are off, current will flow through the annunciator lights through the turn signal lamps filaments to their grounds, so long as the lamps are off.

Anyway UPDATE:

Pulled the cluster this morning. Most of the screws holding the metal back plates were either loose or missing. Replaced the screws, tightened, and ran a separate ground wire from two spots on the back plane to the chassis. All works correctly now.

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