What terryb said is correct. In other words... The first ball that is locked should close the lower switch, then the second ball would close the middle, then the third ball would close the upper.
Another way to test this would be in switch levels test (right after switch edges in the test menu). Drop a ball into the vault and see which switch it holds closed. I believe it should hold the lower swamp lock closed. If not, they are probably in the wrong order.
Derek