[Ken Henry]

Sorry to hear that it's still not working. Assuming #4 is the correct terminal on the overdrive solenoid, using a toggle switch to that should directly energize at and engage the overdrive when you lift off the accelerator. You've bypassed all the additional complexity which is good. When you push the overdrive lockout cable in does the arm on the overdrive shifts all the way back toward the tail shaft (is it properly adjusted to allow full movement of the OD lockout arm?). It seems like it might be something internal unfortunately... Ken