The switch can be put in two ways. I use the three position switch. In the center it's "off". Lock up will not occur or if it's being driven in the "stock" mode, & it's locked up, center will unlock the TC. I usually start off in "off" and move it to what I call "manual lockup" (forward) when I feel it's time for lock up. In this position, it stays locked even when you tap the brake or let your foot off the accelerator, and stays locked until you move back to the "off" position. There is some confusion about what's happening when you feel your truck "shift". Some think what they feel when the TC locks is OD. The trucks shifts 1st,2nd,Drive,OD, THEN it locks up. Lockup is the last big RPM drop you feel, not OD. If you have OD turned off, then Lockup happens in "D" or 3rd. With the TC manually locked, you get engine braking when going down hill or coasting to a stop, rather than freewheeling when you take your foot off the pedal ... ... . DDG