Hi there and thanks for the positive words on my FIN1010 and FIN1012 related work! It is still an exciting journey and almost daily interesting learning! Cool to see, that others out there also have some interest in these systems!
My focus in this thread is the LTN-72RH I obtained to see the difference to the UK made Ferrantis, so I do not have got any information spcific for your LTN-51 CDU and maybe this pinout (acquired with the help from the nice guys here - THX!) does not match your CDU (although it also has got two plugs, your known pins do not the pinout I have got). So probably not of much help for you:
Just out of curiosity: Do you have got a LTN-51 and what are your plans? Do you want to fire it up or are you just interested in lighting up the CDU for some purpose?