Engine shaking/ rough

Posted a few weeks ago about a violent shake at idle. So far ive replaced valve cover gaskets(oil in plug bores and on coils), cleaned the tb, maf, replaced spark plugs, and cut the split ends off my vacuum lines. I pulled codes for o2 sensors, catalytic converters, and secondary ignition fault. I purchased a new coil and moved it to all 6 positions. I did find one coil that had rust on the contact spring and on the outside of the coil body. I thought that would have been the culprit but no change. I have new sensors coming by the end of the week. Does anyone know where the grounding wires are for the coil plugs? Next move is to clean/ inspect wiring in Hope's of a faulty ground.