This is how they work,
On an overdrive the relay was used to supply power to the OD solenoid. When you floored the throttle pedal a switch under the pedal closed a circuit to a set of grounding points inside the OD solenoid. The other side of the circuit was connected to the coil primary on the distributor side. The kickdown switch also killed power to the OD solenoid. So the solenoid is not energized and the ignition circuit is interupted. With no torque on the sun gear, the spring inside the OD solenoid is able to retract the pawl that was locking the sun gear to the case and you go back to direct drive. Retracting the solenoid also opens that set of points that allowed the ignition to be interrupted. It all happens in a split second and you never notice the ignition being interrupted.
So what you need is the working parts in the overdrive unit and a kick down switch. No external relay is needed. If try do wire it with any other way, the ignition will be shut off every time the throttle is wide open. The spring paw in the overdrive retracts turning the ignition back on, this is the key! You need the ignition back on ASAP once the overdrive disengages.
Last edited by Joe H; 11/25/2025 4:05 PM.
