OVP or MAS relay, depening on which one you have.

The overvoltage relay has failed, causing trouble with intermittant power supply to the engine controls and leaving the speedo dead (it's electronic on that model).

Check the fuses and replace the relay (hopefully just an OVP relay, the MAS one is pretty pricey).

You can check for lack of power or voltage fluctuations to test it if you dont' want to just buy one and sway to see.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!