Tach and Transmission Shift Problems
 

95 2500 cumins diesel automatic. The tach stooped working and the transmission will not shift into the higher gears. I have no 8v reference at the vehicle speed sensor. I swapped PCMs with another truck, no change. The functional truck has 8v at the PCM pin 7 orange wire. The failed truck does not (key on or running). Where does the 8v come from? Does something else tell the 8v to turn on. Any Help or Ideas would be great.