Yes when lock-up first came out they were all hydraulic as they used gov pressure to move one of the valves so the car had to be over a certain speed and it had to be in third gear on them. You could change a spring to raise when it locked up. Then around 1986 they went to the electrical solenoid
since they were now using computers on the cars and it made it easier to have control over when the lock-up came on as the computer (PCM) can moniter all the systems better like eng speed , vehicle speed , eng temp , eng vac and the throttle posistion by the TPS. It is still partial hydraulic as it still has to have shifted into second to feed pressure to the solenoid and it has to be in third so the fail safe valve gets pressure to move. They can still control when it applies by turning on the last item needed to move the lock-up valve over which is the solenoid. It can also be confusing how they word things as they call the relay on some the Part throttle unlock relay but really it dont make sense to me as yes it can unlock the lock-up at any part throttle it likes since the computer knows just where the throttle is and all the other inputs it needs to know. So yes the relay can cause it to unlock at part throttle but it can also loc-up or un-lock the converter when ever it likes. Bottom line is on this system the torque converter can not lock-up without the lock-up solenoid being powered on and it can un-lock the converter whenever the PCM turns the solenoid power off. Thats all I was trying to say is no matter what they call the lock-up solenoid or relay it will control the converter to lock-up or un-lock. Ron