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Old 09-18-2008, 02:33 PM
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W126 Fuel Gauge & Temp Gauge

I've got a 1991 560SEL. My temp guage and fuel guage are sometimes erratic. My instrument cluster lights would go out every once in a while too. The other day, my speedo quit, (34 miles short of 200K!) so I pulled the instrument cluster to make sure everything was connected. There's a little green wire with round black connector alongside the main wire going to the speedo (I think) which may have been disconnected at the harness end. I disconnected everything and reconnected everything back up. I did not miss any.

Now, my fuel gauge and temp gauge both go all the way up as soon as I turn on the car, I've got no instrument lights and the speedo is still dead. It's a little tough to tell how much gas I've got left!

I checked fuses. Does anyone have any ideas where to start? I'd like to at least get the fuel gauge fixed!

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Old 09-18-2008, 02:43 PM
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I would check the ground wires. They are brown and connect to a bolt behind the cluster.
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Old 09-19-2008, 07:15 AM
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Ok, so I checked ground wires. Everything seems fine. I search instrument cluster problems again and saw a thread that mentions that the fuel gauge and temp gauge use the same ground. Someone else suggested adding a completely separate ground wire to the cluster. I did this and viola! the guages came back. Still no instrument lights or speedo. I'm thinking I disturbed a lead on the back of the light switch itself. As far as the speedo is concerned, I guess I gotta look further.
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Old 09-19-2008, 08:17 AM
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Something like this happened to me a few months back. I removed the cluster to change bulbs out and when I put it back my gauges went crazy. The fuel and temp maxed out and the oil pressure didn't work. I was told to get small alligator clips and put them on the back of the cluster( I put them on some studs behind the gauges) and then hook them to the main grounds. That cured the problem. Eventually, I took the leads off and didn't need them anymore. I'm not sure what happened originally and why the problem fixed itself though.
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Old 09-19-2008, 09:58 AM
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Pretty much exactly what I did. Three small studs with nuts poking out on the fuel gauge end in the back of the instrument cluster. I attached a wire to one and attached the other end to the main ground wires behind the cluster. That brought back the two gauges.
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Old 09-23-2008, 11:42 AM
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The spedo on the w126 are electric and I believe there is a sensor on the rear of the transmission that sends the signal. maybe the wire or connector is loose.


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