I hooked up a vacuum switch to control the convertor on a Chevelle that I had put a 200 4R into. It really didn't work all that well for me. It was a little too busy locking and unlocking the convertor while cruising. So the next time I put in an overdrive with a lockup convertor I just wired it so that it would automaticly lock up the convertor when the tranny shifted into overdrive. It seemed to work just fine like that.