I made this from a GM "key left in ignition buzzer". It is great when you are working alone and need to check a circuit like an electric fuel pump or starter . Just clamp it to ground and attach the red lead to the circuit that should have power to it and then jump in the car and turn on the key and listen for the buzz. It is especially helpfull when trying to diagnose electric fuel pumps because they have a short prime mode and if the engine isn't running the computer shuts the fuel pump off because it sees no oil pressure. If you do have power it means that you will have to drop the tank and find out why the pump is not pumping fuel. If you don't have power then it is obviously and electrical problem up line and you should not need to drop the tank. It is polarity sensitive so make sure you hok the red lead to the positive side of the circuit or you will not hear the buzzer. I've made a few extras to give to my special friends that do automotive work.