You are too kind. In fact I have misplaced most of the information on these cables over the years. In general though the 1/8 mono plug that goes into a 505-501 or the 8 lane adapter on a 503 should be:
Tip = signal = pin 2 DB9
Ring (sleeve) = ground = pin 5 DB9
Make one up and try it. If it doesn't work, reverse the wires at the DB 9 end and try again.
Write us back and let people know what worked.