Shifter cable installation 1969 cutlass s convertible

OK, OK, I hate to admit this, but I am stumped. There must be a method to the maddness, I just don’t know what it is. I have a 69 Cutlass S with the 350 engine automatic trans which has a floor mounted shifter & console. The problem is that I can’t get the cable to shift the right way. The trans does shift if I do disconnect the cable & shift it by hand, so I know the trans is OK. I know there is a “trick” when installing these GM cables, just can’t remember what it is. HELP !