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mercedes 300E.1988.
The fuel pump has a mind of its own.We have replaced the relay and cleaned all the wiring.All fuses have been replaced.Sometimes it will work ,other times dead as a door nail.The pump has only done 24.000 km,was replaced in aug 2007,car is not used much last 3 yrs.

If you are getting 12 volts to the pump and the earth is good, it sounds like a faulty pump. Even a new pump can cause problems - particularly if it hasn't been getting much use.