Now undo it and clean up the earth point and all the terminals with emery or wet and dry, refit. The do the same the other side. Then do every other earth point and connector plug you can find. That should prevent further, similar, problems.
Good - Fast - Cheap: Pick any two.
E23 735i; E30 318i; E32 735iL; E38 735iL; R50 Cooper; R55 Cooper Clubman.
E21 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i