I've just noticed it written vertically at the amps . I thought the plug in
amps themselves were identical. Taking a closer look one is marked LF
6479e-01
and the other b instead of e, will have to look at the SM as otherwise
physically look the same. Just as well I marked where each came from as I
thiought they were interchangeable. But then as long as an "unmatched" pair
then would it matter which way round, assuming the ERR line worked correctly