I think I have an unique problem. I have a 4"x4"x6' space which is all wall board above a pass through. I have 3 small wall sconces I want to mount above the pass through. The problem is the wall board. How do I attach the electrical boxes so I can mount the light fixtures? At this point I have the lights working but they are attached directly to the wallboard and they are not fully secure.
mbd281

I think I have an unique problem. I have a 4"x4"x6' space which is all wall board above a pass through. I have 3 small wall sconces I want to mount above the pass through. The problem is the wall board. How do I attach the electrical boxes so I can mount the light fixtures? At this point I have the lights working but they are attached directly to the wallboard and they are not fully secure.
mbd281
Is this passthru an interior framed wall or just cabinet work. Does the pass through have a rollup or pocket door? Or no door at all?
The light fixtures must be attached to a qualified electrical outlet box if this is hooked up to a standard 120vac wall outlet. If this is a light fixure that has its own fixture cord and plug, then mounting a sconce against the wall will need a high mounted receptacle outlet or the cord is going to need to be attached away from the opening. Need more information to fill in what really needs to be done. Nm

What you need is called an old work box or cut in box, either metal for BX or plastic for Romex. Any old work box has ears that prevent the box from falling into the wall cavity.

Metal boxes usually need box supports to keep them in the wall. Plastic, and some metal boxes, have screws that have something similar to a wing toggle that will draw the box tight to the wall from inside.

See the picture of a plastic box for Romex cable only.