I took down a lighting fixture to upgrade and found out there is no junction box in the wall. I can put in a junction box as I have done it before. But the center point that matches up with the sink is a good 5 inches from the 2x4. How do I attach a junction box away from the 2x4 and then how would I patch up the reamining hole? Do patch up the hole first then make cut out for box or put the box in first then patch. Here is a picture of what I have. Thanks
Get an old work box and scribe your circle. Then put a little strip of plywood or whatever next to the circle behind the drywall and screw it on either sides to act as a backing. Put in your drywall patch and cut out your circle. Because an old work box sticks out it will be easier for you to tape your patch now. Sand it, prime it, paint it, then install your box. If your installing a heavy fixture i would cut out joist to joist and put a 2x4 between and throw a pancake on that. Hope this helps.