Erratic Fuel Gauge

What could be the reason for my fuel gauge needle to "suddenly" start wandering back and forth, with readings varying by as much as a quarter
of a tank? Whether I am driving, or idling, I watch as it wanders from 1/2 full, to 1/4 full and back again??? Just Started!!!??
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Fuel gauge is electric so a poor connection, including ground, would account for such erratic behavior. The gauge or the tank's sending unit are the next suspects.
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snipped-for-privacy@webtv.net (r parris) wrote:

You didn't give the year of your MBZ. Mine's a '76. If yours is as old as mine, and you went into your trunk, pulled back the cover and pulled out the sending unit you'd find yourself looking at a cylindrical housing that can be screwed off (there are a couple of small holes near the bottom of the cylinder that allows the fuel to seep into the housing. This was MBZ's way of dampening the motion of the float in the sender whenever the fuel in the tank started sloshing around).
Once the housing is off you'd see that the float is like an elevator. It rides up and down between two wires. The wires are part of the electrical system of the sending unit. If they or the points of contact between the float and the wires get fouled, you'll get erratic output to your gauge.
It's an easy task to clean the wires and contacts to see if that is the cause of your problem but take care not to stress the wires to the breaking point in the process.
Lots of luck.
ron
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Car is 1992, 190E 2.6 with 135,000 miles. I now notice, heavy (white ashy) corrosion on nuts of recently replaced upper strut mounts where a ground wire connects!!? ...... loose bolts?
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