I have an 86 D150 and it has a one wire electrical plug going in thru the main case close to where the tail shaft bolts on to the main case of the trans. It has one solenoid mounted to the valvebody. Im told this confirms its a lockup trans. Hope that helps!
If its a round connector at the left rear of the trans then yes it sounds like it is lock-up. I believe that model also uses a relay for the lock-up as they called the relay a part throttle unlock relay but it locks and unlocks the converter and the relay is controlled by the PCM (eng controller). The relay should be mounted on the firewall and it sends power to the lock-up solenoid in the trans as the solenoid on that one is grounded in the trans as it only has the one power wire to it from the relay. Ron
