The OVP relay and fuel pump relay are probably the cause of your problems. Both can be disassembled and repaired. There are usually a few broken solder joints that just need to be re-soldered. I usually re-solder all of the joints just to be sure that they are all good.

The relays can be a bit tricky to get apart, but you just need to be patient and use a few small flat blade screwdrivers to get the covers off of the relay's circuit board.

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1992 300D 2.5 TURBO

1991 560SEL M119.960

1986 300SDL TURBO