Check the voltage across the battery. Should be 12.5 V with the engine off, 13.1 or higher running, but less that 14.1.

Get a new regulator, but you may have a bad diode or two -- needs a run on a test stand to verify.

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!