If you are trying to figure out one or two pins at the trans. connector this wil help.
http://67-72chevytrucks.com/vboard/s....php?p=7037666
Since you are retrofitting a TH400 just install the 71-72 style detent switch on the accelerator pedal and run a couple of wires or buy a harness for a 71-72 and be done with it. No need to install an aftermarket cable switch when stock (as on a big block TH400 or C30 installation) is easily done.