fluorescent light wiring question

Based on the bulbs (T12), I believe I have a dead ballast in a laundry room fluorescent fixture. I purchased LED replacements and need to rewire the fixture to bypass the ballast and starter and install non-shunted tombstones. It seemed fairly straightforward until I took down the fixture, I spotted a very strange wiring arrangement. There is a metal box of unknown purpose with some rather narrow gauge wires connected to it. The Romex coming from the switch for the fixture has it's hot wire (black) routed to it as well and a black wire comes back out which was twisted with the white neutral wire from the Romex. There is also a red wire with the Romex. When the switch is off, I used a current tester and the black wire coming from the mystery box is live. I cannot figure out where the mystery box's narrow gauge brown wires go to / come from. Even with the switch off, I believe the Romex black wire is live due to this wiring arrangement. Please help! I can try taking better pictures if it helps. Attachment 43495 (http://www.doityourself.com/forum/attachments/lighting-light-fixtures-ceiling-exhaust-fans/43495-fluorescent-light-wiring-question-2014-12-19-16.15.54.jpg)