50 amp fuses were used on most 123 240D diesel glow plug systems due to the lower amp draw. 80 amp fuses will also work but some may choose to go with original spec. Check the number on the center of the fuse you are currently using. It should read either 50 or 80.
For 1977 to 1983 240D
50 AMP Glow Plug Circuit Strip Fuse - Sold Individually