Don't do a diagram, do a spreadsheet. Terminal numbers as (text) column headers and row values, then a grid of measurements at each row/column intersection. Obviously the diagonal where row=column will be blank. Enter shorts as 0 and leave opens blank.
Always put the positive probe on the row label terminal so the results will meaningfully show the presence of any diode junctions, i.e if resistance(col,row)<>resistance(row,col)
Also, *HOW* is the box sealed? some good photos of the sides may lead to suggestions for opening it non-destructively.
What does it weigh, and what are its dimensions?
What does it sound like if you tap it with a hard object? e.g. does it click, clank or ring.
Estimate where its center of gravity (C.G.) is by rolling it across a round toothpick, and marking the position of the toothpick when it tips. Do this in both directions across a long side, and both directions across the base.
If its heavy and the C.G. is fairly central, perhaps biased a bit towards the base, it would make gbaddeley's transformer suggestion more likely.