Passenger side firewall, the center (I think) Bakelite "box". There are two, the one that goes first is usually the one for the fan, towards the engine.

Clean contacts properly, and replace with a ceramic fuse, not a plastic one, they melt sometimes and get loose (mine did).

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!