Electricity is the movement of electrons through a conductor. Electrons are attracted to protons. Since we have excess electrons on the other end of the conductor, we have many electrons being attracted to the protons. This attraction sort of pushes the electrons toward the protons. This push is normally called electrical pressure. The amount of electrical pressure is determined by the number of electrons that are attracted to protons.
The electrical pressure or electromotive force (EMF) attempts to push an electron out of its orbit and toward the excess protons. If an electron is freed from its orbit, the atom acquires a positive charge because it now has one more proton than it has electrons. The unbalanced atom or ion attempts to return to its balanced state so it will attract electrons from the orbit of other balanced atoms. This starts a chain reaction as one atom captures an electron and another releases an electron. As this action continues to occur, electrons will flow through the conductor. A stream of free electrons forms and an electrical current is started.
This does not mean a single electron travels the length of the insulator, it means the overall effect is electrons moving in one direction. All this happens at the speed of light. The strength of the electron flow is dependant on the potential difference or voltage.
The three elements of electricity are voltage, current, and resistance. How these three elements interrelate governs the behavior of electricity. Once the you comprehend the laws that govern electricity, understanding the function and operation of the various automotive electrical systems is an easier task.
So far we have described current as the movement of electrons through a conductor. Electrons are negatively charged particles that move toward something that is positively charged. Electrons move because of this potential difference. This describes one of the common theories about current flow. The electron theory states that since electrons are negatively charged, current flows from the most negative to the most positive point within an electrical circuit. In other words, current flows from negative to positive. This theory is widely accepted by the electronic industry.
Another current flow theory is called the conventional theory. This states that current flows from positive to negative. The basic idea behind this theory is simply that although electrons move toward the protons, the energy or force that is released as the electrons move begins at the point where the first electron moved to the most positive charge. As electrons continue to move in one direction, the released energy moves in the opposite direction. This theory is the oldest theory and serves as the basis for most electrical diagrams.
Trying to make sense of it all may be difficult for you. It is also difficult for scientists and engineers. In fact, another theory has been developed to explain the mysteries of current flow. This theory is called the hole-flow theory and is actually based on both electron theory and the conventional theory.
Fortunately, it really doesn't matter as long as you know what current flow is and what affects it. From this understanding you will be able to figure out how the circuit basically works, how to test it. and how to repair it.