[rotorwrench]

It's an electrically operated system so it needs to have functional switches, relay, and solenoid for it all to work properly. When the cable is pulled out, the lockout rail effectively moves the sun gear out of mesh an blocks the operating solenoid pawl that does the shifting of the OD planetary. In other words it works pretty much like any manual 3-speed when locked out. When you shift the car into reverse whether the cable is pulled or not, there is a mechanical mechanism in the reverse shift that pushes the lock out rail so that is will always be locked out in reverse.

The firewall mounted relay is the control relay that turns the operating solenoid on & off. The free wheeling clutch has to be there for the overdrive to shift so it has to be fully functional when the unit is locked in with the cable pushed all the way in. The governor on the tail housing has a simple switch to turn the system on when it reaches on speed around 23 MPH.

Ford recommended using the OD as a semi automatic transmission when driving around town. You just leave the car in second gear and only use the clutch when you stop. Starting in second is possible when the car is not loaded too heavily. This way a person can drive away from the stop and let up on the throttle above 23 MPH and it will shift into overdrive. It's basically operating as a 2-speed transmission with a clutch. Whether this works or not depends on the speed limits where the car is operated and is not necessarily the best way to operate it if conditions don't match up well with those speeds.

There are a lot of tests that can be done on the system if something isn't functioning as it should. I would recommend getting the shop manual for the type car you have. there should be a full section of the overdrive system that includes the test procedures. Jumper leads and a test light is all that is required to perform most tests.

The operating solenoid only has two terminals on it but they both perform different functions. Grounding is provided by the drive train to battery ground connection. One terminal is an ignition coil kill circuit for the downshift function and the other is to function the operating solenoid to shift the transmission into and out of overdrive.

There are other threads on here that have wiring diagrams or you can find them on line. If the system is going into overdrive then the kick down switch under the throttle pedal has to be depressed all the way to get it to downshift out of OD. It will also drop out of overdrive when the speed of the vehicle drops below the ON Speed of the governor. It should be out of overdrive any time you come to a complete stop. When it shifts in, you will notice the drop in rpm. If you don't feel it going into overdrive planetary gear then it isn't working correctly. The kick down switch, governor switch, and relay all have to be working. Some of the older units also have a rail switch in line with the governor switch control that can give problems. Later models eliminated that switch as redundant. It can be bypassed if it's not working properly.