Something is wrong with the wiring in my shed, I think. I'm pretty sure that it's been wrong since the previous occupants lived here, and maybe even earlier than that.
When I moved in there was clear evidence of scorching in the shed - apparently something had melted and caught fire. I'm sure it was a rather exciting time. I replaced the damaged wiring and the receptacles, but when we were trying to wire things up correctly we could not figure out the correct order of the wires. It doesn't help that they're all gray wires. We spend a lot of time scratching our heads and puzzling, and then I realized that at most we had 6 different combinations, so we tried each paring and finally figured out that at least one of them was ground, but we still couldn't figure out which was hot and which was neutral. So we just wired things up and the only thing I plugged in was an incandescent lightbulb.
Recently I've thought to revisit the shed wiring and have discovered something that seems rather strange. Between ground and one side, I'm reading ~240v, and ground and the other side I'm getting ~120v.
I'm not sure what they're supposed to read, but on another outlet between ground and neutral I don't get any reading, and ground and hot I get 120v.
120v Between Hot and Ground
240v Between Neutral and Ground
My Dummy Light is Confused, Too
You may not be able to see the label clear enough, but my dummy light has all three lights on - but that doesn't correspond to any of the options on the label.
So I'm terribly confused as to what's going on here. How would I find and fix the issue here? I'm assuming it's probably in my circuit box - I took it off once before, so I know where it is and a little about it. I don't have the option to shut off the mains electricity to the house, so if I were to undertake such a fix, what safety precautions should I take? (If the outlets don't make it clear enough, I'm in the United States)
Inside My Breaker Box
On the right side you can see three wires coming in through the back of the box: they go up to the 20A circuit breaker on the right side and to the ground rail - those are the wires that go out to the shed.