the grounds should be brown wires, they will be grounded to the chassis , on my 81 240d the tail light ground wire is at the lower part of the light box in the trunk area, there are several ground wires behind the instument cluster, also make sure your fuse box contacts are clean and you upgrade to the copper tip fuses...
Gretchen 1981 240D 4-spd 213,000 mi
1979 240D 4-spd 298,000 mi parts car
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