I have a 700r4 with no computer. OVerdrive is jsut 4th gear, nothing required to make it kick in. There are 4 pins on the tranny, two can be shorted together, usign a toggle switch, to lock the tranny in over drive (4th gear) but you have to manualy have to release the short. I have seen hardware that goes in line with the speedo cable and hooks to those two terminals and autamatically locks/unlocks the OD. Try Ron Francis Wiring.