Here's a possibility:
There are 2 thin black wires that pass through the tubular shifter from the O/D
Cancel switch. As they exit the hollow shifter, they make a 90 degree turn before traveling down the top of the steering column. At higher miles, it is fairly common for those wires to chafe and/or break from repeated shifter movement. Check fuse #6 in the dash box and remove the top column trim to inspect the wires.