You are confusing fuse number with terminal number.

MB numbers the wire connections by function. #50 is the starter circuit, #15 is "ignition on". The numbers are stamped in the metal or molded into the plastic parts of the fuse box, underneath where you want to attach the wires. Couple screws hold the fuse holder in the box, remove and pull the holder up and turn upside down.

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!