Check battery cables and ground connection at the engine and frame first, but if you don't find anything, have the starter current draw checked. If it pulls too much current, replace it before it refuses to start the car in cold weather.

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!