You'll see how the switch and bracket are connected to the carb. The curved tang on your carb arm makes contact with the switch when 3/4 open throttle. There are two wires from the swicth. One connects to 12V (you can tie into your wiper motor) and the other runs to the solenoid. All the switch does is send an electrical signal to the solenoid in the trans making is shift down. Pretty simple design.
