Sure the later ones use a solenoid in the trans. All the early ones when they first came out in Mopars were hydraulic as I remember a 1979 Aspen I believe that was all hydraulic. I dont remember what year they started using the solenoid in the valve body so the PCM could control lock-up but I know my dads 88 truck had the electric lock-up solenoid in it as that year just had a one wire plug on the left rear of the trans main housing. The solenoid just controlled a bleed off (vent) of fluid pressure to the lock-up valve. John Kunkel will know which year they started with the electric solenoid in the valve body but I dont remember myself right now. Ron