I'm installing a new medicine cabinet and a small sconce in my old NYC bathroom. The walls are lath and plaster, and I have already removed the 1940's cabinet that was recessed. I sheet rocked up the hole, and want to use the original sconce electrical mount and keep the 2 socket outlet that's already on the wall. I cannot open the wall to do any work, and I don't want to/cant replace any of the ancient wiring that exists. The cabinet is a wall-mount unit and has built in lights and a single socket, prewired by the manufacturer with two pairs and a ground wire that I need to connect to power as well. Without ripping out all electric and replacing/re-running wiring (not allowed by building), how can I safely wire the cabinet, wall sconce and existing outlet? Thanks in advance!