I am adding a new ceiling light to a switch that currently controls a switched outlet. I have already unswitched the outlet and am getting ready fish down the new wire from the ceiling light, but seem to think it would be easier to put in new old work gang box and cut out the metal box instead of using the knock out and having to open abaove the current gang box location. My question is, my house does not have ground wires in cable runs, only grounding to each metal gang box; how would I ground the new ceiling light in the ceiling box is old work plastic and the gang box it is attached to is old work plastic? The new wire I ran does have a ground wire running from ceiling to existing gang box.