I would suggest avoiding a 1 wire alt & instead get a 78 amp alt for an 85 M body. it has the thin stator (ribbed section inbetween the two cases) so a slight spacer adjustment will be needed & possibly a slight swing arm adjustment but no big deal. for a true bolt in just get the highest amp alt they have with the regular width stator & what DVR said ground one of the male field terminals to one of the (3) case halves mini bolts with a ring terminal and brass 1/4 female terminal (NAPA 725145) 99 cents + tax & a short pigtail piece of wire then run your regular long green field wire from reg up to other alt field terminal