Thanks, David! I took the box off this weekend to inspect it and wowee - I'm surprised it didn't short out when I first tested it. The wiring was really bad.
I'll borrow your technique for removing the rivet and see how that goes. I had already designed a replacement junction box using a split-wired outlet and a surface-style outlet box but I'd love to keep the original one if I can.
Here's what the box looked like on removal and how scary the wiring really was.


I'll borrow your technique for removing the rivet and see how that goes. I had already designed a replacement junction box using a split-wired outlet and a surface-style outlet box but I'd love to keep the original one if I can.
Here's what the box looked like on removal and how scary the wiring really was.

