A clamp is placed over the #1 injector line, when the pump sends fuel, it sends a signal to the box. The box triggers a signal to go through the high tension lead(loop) that you put your inductive pickup from your timing light on. That makes the timing light flash. Then you use your timing light just like on a gas engine. If you have an advance light, you dial in how much advance you need, then make the marks line up on 0 degrees on the damper.