All of my switches are installed in old metal boxes with no threaded ground screw holes. The boxes are wired using old cloth BX with no ground wire(grounded via casing). Some of the BX wire insulation is crumbling near light fixtures, I think due to heat.
As I replace the light fixtures I'd like to replace the BX from light to box with Romex. The BX that supplies the box is in good shape. How do I appropriately ground the new fixtures. There are no threaded holes in the metal boxes. Grounding to the box via the yoke on new switches will work but I don't think this is proper. Can I just tap a new 10-32 hole in the box? Should I tear out all of the old bx or maybe just run new ground wires? Thanks in advance.