so here's how it works. There are three wires on the connector at the transmission. Purple is 12V+, brown is ground, and green is the 3rd/4th gear signal to the ECM. The purple wire is routed through the brake light switch to supply 12V+ from the gauge fuse to the lock-up solenoid any time the brake pedal is all the way up. The brown wire is goes to the ECM, and it grounds the solenoid whenever the correct conditions are met for lock-up. On pre-ECM cars, the brown wire went to a ported vacuum switch which locked the converter when you were driving with above 10in-hg manifold vacuum. They also used a pressure switch in the transmission which only allowed lock-up in high gear.

Anywho, with no ECM, the green wire is meaningless to you. Leave the purple wire as-is. Install a toggle switch between the brown wire and ground to lock up the converter. It's also a good idea to make sure you have a 3rd gear pressure switch so that the converter will only lock-up in third and so it unlocks if you accidentally kick it down into second gear and forget to flip the switch