The cable controls the freewheel over running clutch inside the trans. Whith it locked, the trans works like a regular 3 speed. Unlocked, it allows the trans to shift into overdrive at roughly 28 mph, once you let off the gas for a bit to releive the torque load. This isn;t an exact speed, as it will vary depending on rear gear and tire size. You also have the option of free wheeling (no compression braking) when the overdrive isn't engaged but the over running clutch is unlocked (cable in).
The solenoid is what actually engages the overdrive gearset, it has 2 wires on it. 1 wire is the actuator wire (green on original harness) which is the pull in part, then a second which runs at a lower amperage that is the hold in, which keeps it locked in. There is also another wire in the system, and that is the governor. The governor wire connects to the ground side of the relay, and activates it when the cut in speed is reached. All of these wires lead back to a kickdown switch, which kills the power to the solenoid at roughly 3/4 throttle. Some people run a switch rather than the relay, and count on that to engage the od. I do have a switch on mine, but is connected to the relay, and is set up to operate as the factory intended. Only I can kill the power to it when od is not wanted, and the freewheel is usually locked out too.
The wireing harness is available, and a pto cable works best for the lockuot, however, the kickdown switch is not being repoped, and originals are very pricey. I have one on mine (I won't admit what I paid for it, but it was NOS), but so far, have never had to push it far enough to need to kickdown. The 235s torque is plenty to accellerate without it. As far as a relay goes, you'll want one that can handle at least 30 amps, preferrable with a built in fuse. I used a headlamp relay from Standard-Bluestreak, and hid it under a voltage regulator cover.
These trannies are definetly worth the effort, and drive very nicely while maintaining an original look.
