IF you are still using Original - "Notch" denotes Positive.
Opposite corner denotes NEGATIVE
Between the Notch, opposite corner - is AC Input.
To Verify?
Start at Notch - Place POSITIVE Test lead there.
Then "test" to all other points using Negative Lead.
"any Open"? Might mean "wrong +" at start, which means the test failed.
Wanted to mention - and look carefully - at your photo.