In this case the power still goes through the fuse box but not until the key is on. Now that we have power going to the system we must complete the circuit, so we will need a clean and tight ground connection. The ground system is the most overlooked and neglected part of the electrical system. There must be a good ground from the motor to the battery. There must also be a good ground to the body of the car, and in many cases several grounds to the body.
Lets take a closer look at a very basic electrical system.
We start with a good battery. This is the power source. Then we take a light bulb of a compatible voltage and attach a wire between the center electrode to the positive side of the battery. No, because we must complete the circuit. If there is any interruption in this circuit the bulb will not light.