nothing really wrong with dredging up an old post - as long as no one goes nuts trying to come up with an urgent answer ...
anyway ...
for anyone who might come this way in the future, here is a set of drawings that I drew up to use in my PLC-5 classes - back before I retired ... this approach proved helpful to a lot of folks over the years ... since there are quite a few PLC-5 systems still chugging along out there - maybe this will come in handy ...
be sure to read the notes ...
party on ...
.