I want to replace the 3 "hollywood" bar lights that are each 4' long in our master bath. Want to replace with a newer style vanity that has a 5" circular mounting. The existing mirrors (3) each had a bar light. I have successfully removed the original lights. The bar lights were "double-sided foam taped" on and there is a 2" hole cut in mirror for wire to go through. No outlet box, only the wire coming out of the hole. The hole is too small to do much.
Can I use mirror mastic and just glue the new metal backing/plate? Much of the dry wall behind mirror hole has been damaged as original installer just punched through. I was hoping to add at least one molly-bolt and maybe glue the rest on. Any ideas? Much appreciated! SInzer

What is on the wall behind the Mirror? May be able to do work from behind, and not deal with the mirror. Good Luck.

That sucks. You are in a VERY difficult position. For the style light you are putting up you definitely need a sturdy mounted box. This may be impossible due to the previous install.

The 2" holes in the mirror are a severe setback. Any chance you can get someone in to cut larger holes so real boxes can be installed?

If I understand correctly you have removed a bar type fixture. You have the cable coming through the drywall and all connections were made inside the fixture. You have no electrical box in the wall. You now wish to install a fixture that requires a box. Would your new fixture fit flush to the mirror if you installed surfaced mounted, 1/2" deep, round "pan cake" box?