You really need the original electrical hookup, or a clone, for the unit to work right. There are two electrical devices on the transmission, a "governor" which keeps the OD disengaged below 30 MPH (depending on final drive ratio), and a solenoid to engage the OD. The cable, as mentioned before, is a lockout to allow engine braking going downhill, etc. BTW, don't trust the transmission to act as a lockup for parking in gear, unless you put it in reverse. Under some situations, the car can roll away, even if it's left in gear.
There needs to be a kickdown switch, an idle position sensor switch with both normally-open, and normally-closed positions, and a relay to operate the transmission solenoid. All these things can be duplicated with easily-available electronic-supply store parts, if you have a wiring diagram to follow. Original-equipment parts are scarce, especially the relay box.
Jerry
