BB 727 Trans help please

Ya if it's a switch for two things then a power or ground (either) would have to be the third wire. I guess some testing is in order then, should not be too hard to figure that out in that case. And MRMOPARTECH the motor is a '78 with cast crank so should be ok. I have not even tried to mate trans to motor yet, as my 'cherry-picker' seems to have lost a seal or something. Only wants to work half the time, then drop whenever it wants to..haha, not real safe.